Identifying and Compiling 48-Hour WPR Reports

Researchers first identified the reports Presidents have provided to Congress under section 4(a) of the War Powers Resolution (“48-hour reports”) since the statute’s enactment in 1973, totaling more than 100.20 Researchers then analyzed and compiled the text of each report in the database available on this website. We update the database regularly, and believe it contains an exhaustive set of unclassified 48-hour WPR reports. Nevertheless, we encourage feedback if it appears that we have excluded any such reports in error.

With very few exceptions, Presidents generally do not cite to specific sections of the WPR when providing reports to Congress. Thus, whether a given communication to Congress was coded as having been provided under section 4(a) (a 48-hour report) or under section 4(c) (a periodic report21) was determined based on factors such as whether the report appeared to describe activity that had commenced within the last 48 hours (although a few reports appear to have been submitted late), whether it included the statutorily required information for 48-hour reports under sections 4(a)(3)(A)-(C) of the WPR, whether it described ongoing events or focused on new and discrete activity, and whether the text indicated that the report was intended to provide additional or supplemental information. 

Periodic reports have sometimes noted the existence of a “classified annex,”22 which could indicate that classified 48-hour reports were provided to Congress in the preceding six months covered by that periodic report. In addition, at least one 48-hour report in this dataset, provided by President Obama on March 25, 2014, in relation to counter-Lord’s Resistance Army operations in central Africa, refers to a classified annex to that report. Any classified annexes or fully classified 48-hour reports are necessarily excluded from this database and accompanying analysis.23 

Standardized Coding of 48-Hour Reports

Researchers analyzed specific types of content in each report, including categories of data required to be reported by the WPR, as well as additional types of information that provide further insight into presidential reporting practices and deployments. 

Basic identifying information coded for each report includes the date the communication was provided to Congress, the President who submitted the letter, the presidential term (where applicable for Presidents who served more than one term), and the reported location of the activity.

The following substantive types of information were also coded for each report:

  • The stated purpose or mission (or “circumstances necessitating the introduction”—required under section 4(a)(3)(A) of the WPR).

  • The “constitutional and legislative authority under which” the activity took place (required under section 4(a)(3)(B) of the WPR).

  • The “estimated scope and duration of the hostilities or involvement” (required under section 4(a)(3)(C) of the WPR).

  • The actual duration of the activity, if known.

  • The type of military activity (such as the use of air, naval, or ground forces).

  • The type of enemy or mission (such as whether a state or non-state actor was involved).

  • The prong of section 4(a) of the WPR that triggered the requirement to submit a 48-hour report (introduction into hostilities or imminent hostilities, combat-equipped introduction, and/or substantial enlargement).

  • Whether other 48-hour reports are related to the report at issue.

  • Any indicated international legal basis for the action (and, as applicable for reports in which self-defense is the stated or inferred international legal basis, whether a communication to the United Nations pursuant to Article 51 of the UN Charter was filed).

  • Any U.S. or non-U.S. casualties incurred by the time of filing, if noted in the report.

  • Any reported information regarding whether the activity was part of a coalition or joint mission.

For each of these categories of data, information drawn from the reports was analyzed against a set of structured codes that researchers applied. For example, the “stated purpose or mission” of the activity could be coded as one of the following:

  • Respond to threat

  • Protect U.S. citizens, property

  • Rescue/hostage recovery 

  • Evacuation

  • Humanitarian 

  • Stabilization 

  • Advise/Assist 

  • Other

In order to avoid subjective judgments to the maximum extent possible, in all cases researchers aimed to record the data as presented by the President in the text of the report at issue. Some key areas of analysis, however, require interpreting terms that are contested, such as “hostilities” or “combat-equipped.” For data categories that implicate contested definitions—such as the prong of the WPR that triggered the requirement to submit a 48-hour report (discussed below)—researchers analyzed the reports according to interpretations used by the executive branch to the greatest extent possible. Where definitions do not exist in statute or regulation (and courts have not opined on the meaning of the term), interpretations were deduced from sources such as congressional testimony by executive branch officials, opinions of the Legal Adviser of the Department of State and the Office of Legal Counsel (OLC) of the Department of Justice, and statements and inferences from the reports themselves.24 Nevertheless, coding some of the categories of information required an element of subjective judgment. 

Inclusion of Unstructured Data

For a number of the data categories described above, additional “unstructured” data were also recorded to provide further context and detail. Where possible, this includes excerpted language from the reports themselves.25 

Single and Multiple Field Data Categories

For some types of coded data, multiple entries are possible. For example, the type of enemy may be coded as “non-state actor” and “state actor,” should both codes apply. The WPR 48-hour report trigger is another example, as some reports indicate introduction into hostilities (or imminent involvement in hostilities) in addition to, for example, a combat-equipped deployment. Multiple entries are also frequently used in the “type of military activity” category, for which air operations, use of naval forces or vessels, and use of ground forces may occur alone or in any combination. 

To facilitate analysis, a single code was chosen in recording the purpose or mission of the activity in each report. In some reports, when more than one purpose was potentially appropriate, researchers determined and coded the primary purpose. For example, air patrols reported by President Clinton beginning in 1993 in the context of NATO operations to enforce a “no-fly zone” in Bosnia, authorized by the United Nations, were coded as “stabilization” missions due to the overall nature of the activity, as described in the reports. However, for several of these operations, the “humanitarian” or “advise/assist” categories potentially could also have been applied. In contrast, based on the overall descriptions as provided in the reports themselves, the actions taken in Kosovo in 1999 are coded as “humanitarian.” Descriptions of the activities at issue are provided in the unstructured data.  

Of note, a few reports appeared to provide information about more than one activity that could be considered a report-triggering event. For example, a March 26, 1999, report describing air strikes against the Former Republic of Yugoslavia also reports a deployment for embassy protection in neighboring Macedonia. For the purposes of categorizing the primary purpose of the activity, the report was keyed to the air strikes, which were the main focus of the majority of the report. To the extent there is a secondary purpose for such reports, it is noted in the unstructured data. (Note that when two reports were provided to Congress on the same day, they were identified and coded separately.) 

Coding the WPR 48-Hour Report Trigger

Although the WPR requires Presidents to report to Congress whenever they introduce armed forces into any of the three categories defined in sections 4(a)(1)-(3), Presidents rarely state the prong they believe to be at issue (with the notable exception of the Ford Administration). However, the report-triggering prong at issue is of great importance—not least because only reports under one of the three prongs (introduction into hostilities or imminent hostilities) commences the WPR’s 60-day clock, after which termination of the activity is required unless the activity is authorized by Congress. 

The definition of “hostilities” remains contested, largely due to the significant stakes if the 60-day clock is triggered. The Congressional Research Service describes competing interpretations as follows:

Although the executive branch maintains that hostilities occur only with exchanges of fire between U.S. and enemy forces, the legislative history of the War Powers Resolution refers to hostilities as also including “a state of confrontation in which no shots have been fired but where there is a clear and present danger of armed conflict,” and that imminent hostilities means “a situation in which there is a clear potential either for such a state of confrontation or for actual armed conflict.”26

While the terms “combat equipped” and “substantially enlarge” are not used in provisions tied to the 60-day termination clock, and are thus arguably less freighted with significance, they also remain undefined. 

As a result, determining which prong (or prongs) of section 4(a) of the WPR triggered the requirement to notify Congress required some subjective judgment. As noted above, researchers aimed to record the report trigger by analyzing the text of the report using the executive branch’s own interpretations to the greatest extent possible. In some cases, more than one potential trigger was identified. 

To provide a more granular analysis of this critical information, the data analysis also seeks to illustrate the degree of explicitness with which the trigger was described in a given report. To do so, each of the three statutory report triggers—introduction of forces into hostilities or imminent involvement in hostilities, introduction of combat-equipped forces, or substantial enlargement of an existing combat-equipped deployment—was examined separately. For each potential report trigger, researchers coded whether the report: identified the prong or used the terms in the statute itself (e.g., “hostilities”); described the prong in other language or it otherwise could be inferred from the language of the report (e.g., “exchange of fire”); explicitly stated that the prong was not triggered (e.g., “while equipped for combat, no involvement in hostilities is anticipated”); otherwise described or inferred that the prong at issue was not triggered (e.g., “the mission is purely for humanitarian purposes in response to a natural disaster”); or contained insufficient information to infer the triggering prong.27

Data Coding Consistency Checks

After the data from each report were coded according to the process described above, an additional RCLS researcher checked the full dataset for consistency and accuracy. In addition, several expert reviewers with significant experience in the executive branch related to war powers issues provided additional spot checks of the dataset’s structure and coding. 

Significant Military Activity Not Reflected in Dataset

It is important to note the significant uses of U.S. armed forces abroad that are not fully captured by this dataset. Ongoing military activity, once notified in an initial 48-hour report, is subsequently reported only under the WPR’s section 4(c) periodic reporting provision, which requires the President to provide Congress with information at least every six months on the status of the hostilities and their scope and duration.28 

Perhaps the largest components of the U.S. military footprint that are not fully illuminated by this dataset are U.S. operations in Iraq following the 2003 invasion29 (reported on March 21, 2003) and the sprawling post-9/11 counterterrorism operations authorized by the 2001 Authorization for Use of Military Force (2001 AUMF).30 With respect to the latter, after President W. Bush’s initial 48-hour report in 2001, a number of new enemies have been folded into the conflict under expansive interpretations of the 2001 AUMF, ranging from al-Qaida in the Arabian Peninsula (AQAP) in Yemen to the Islamic State of Iraq and the Levant (ISIL). While Presidents have provided further information in periodic reporting, the executive branch has taken the position that 48-hour reports are not required when armed forces are deployed with congressional authorization. On this view, the broader the interpretation of the statutory authorization—here, the 2001 AUMF—the less WPR reporting will be required, even though military activity continues and in this case has significantly expanded since it was initially reported over 18 years ago.31

Finally, covert operations, which the executive branch has long believed are not covered by the WPR at all as the statute applies only to “U.S. Armed Forces,” are also not reflected in 48-hour reporting under the WPR.32 

Unreported Activity

The dataset described above is the one presented in the project website’s interactive graphics and searchable database. However, in addition to that primary dataset, RCLS researchers used two Congressional Research Service (CRS) reports to identify U.S. military activity abroad that was not reported to Congress under the WPR.33 The unreported activity analyzed for these purposes consists solely of the instances contained in these two CRS reports—as described in those reports, it is not an exhaustive list of military activity undertaken abroad. Nevertheless, this sample of unreported activity provides insight into some of the types of military activity that are not captured by the current WPR framework. 

The unreported activity sample was coded using the same categories as the WPR-reported activity to the greatest extent possible.34 Some findings and observations from this data are characterized in the key findings and analysis section, in a section entitled “Unreported Activity.” However, the unreported data is not part of the searchable database, which contains only reports that were submitted to Congress. 


See U.S. Const. art. II, § 2, cl. 1 (“The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States.”). Congress’ war powers are enumerated in Article I. See U.S. Const. art. I, § 8, cl. 11 (authority to declare war, grant letters of marque and reprisal, and make rules governing capture on land and water); id cl. 12 (authority to fund military operations); id cl. 13 (authority to provide and maintain a navy); id cl. 14 (authority to make rules regulating land and naval forces); id. cl. 15, 16 (authority relating to raising and providing for militias); id. cl. 18 (authority to “make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this Constitution in the government of the United States”).


Brian Egan & Tess Bridgeman, Top Experts’ Backgrounder: Military Action Against Iran and US Domestic Law, Just Security (June 21, 2019), Scholar John Hart Ely explained this decision as “a determination not to let such decisions be taken easily,” or for unpopular purposes. John Hart Ely, War and Responsibility: Constitutional Lessons of Vietnam and Its Aftermath 3–4 (1993) (“The founders didn’t need a Vietnam to teach them that wars unsupported by the people at large are unlikely to succeed.”). And Professor David Golove notes that this feature ensures the elected officials closest to the people have an opportunity for meaningful consideration—the House of Representatives, in particular, “had a vital role to play in restraining military conflict.” David Golove, The American Founding and Global Justice: Hamiltonian and Jeffersonian Approaches, 57 Va. J. Int’l L. 621, 625 (2018) (“The people, [the Founders] imagined, were pacifistic and would resist wars and the human suffering and taxes that military ventures inevitably produced.”).


For a concise overview of the historical position on the President’s authority to initiate the use of force without congressional authorization, the contemporaneous test, and a maximalist position expressed during the W. Bush Administration, see Marty Lederman, Syria Insta-Symposium: Marty Lederman Part I–The Constitution, the Charter, and Their Intersection, Opinio Juris, (Jan. 9, 2013),


Tess Bridgeman & Stephen Pomper, Introduction: The War Powers Resolution, Tex. Nat’l Security Rev.: Pol’y Roundtable (Nov. 14, 2019),; see also Curtis Bradley & Jack Goldsmith, OLC’s Meaningless ‘National Interests’ Test for the Legality of Presidential Uses of Force, Lawfare (June 5, 2018),


Bridgeman & Pomper, supra note 4. As former senior State Department official Todd Buchwald has described it:

[T]he two-pronged test that the Justice Department’s Office of Legal Counsel (OLC) has articulated is remarkably elastic and easily satisfied. . . . On its face, the first prong would only bar cases in which it could be shown that the President was unreasonable in concluding that a use of force was in the national interest. The debate about the reasonableness of any such determination is well worth having but is on its face political in nature. The second prong depends on “the anticipated nature, scope, and duration of the operations [being] sufficiently limited,” but “anticipated” is a funny word. Different actors will doubtless anticipate different outcomes.

Todd Buchwald, Anticipating the President’s Way Around the War Powers Resolution on Iran: Lessons of the 1980s Tanker Wars, Just Security (June 28, 2019),


At the time of the WPR’s passage, “[m]ost Members of Congress agreed that the President as Commander in Chief had power to lead the U.S. forces once the decision to wage war had been made, to defend the nation against attack, and perhaps in some instances to take other action such as rescuing American citizens.” Matthew C. Weed, Cong. Research Serv., R42699, The War Powers Resolution: Concepts and Practice 7 (2019).


See April 2018 Airstrikes Against Syrian Chemical-Weapons Facilities, 42 Op. O.L.C. slip op. at 9 (2018),; see also Deployment of United States Armed Forces into Haiti, 18 Op. O.L.C. 173, 173, 177–79 (1994), The executive branch has recognized that use of force against state actors (as opposed to within the territory of another state with its consent), or where there is a high likelihood of escalation, are more likely to meet this test.


War Powers Resolution, Pub. L. No. 93-148, 87 Stat. 555 (1973).


The WPR’s stated purpose is “to fulfill the intent of the framers of the Constitution of the United States and insure that the collective judgment of both the Congress and the President will apply to the introduction of United States Armed Forces into hostilities [or] situations where imminent involvement in hostilities is clearly indicated by the circumstances…” Id. § 2(a). In contrast to the contemporary view expressed by the executive branch, the WPR provides that the President has authority to introduce U.S. armed forces into hostilities, or situations where involvement in hostilities is imminent, “only pursuant to (1) a declaration of war, (2) specific statutory authorization, or (3) a national emergency created by an attack upon the United States, its territories or possessions, or its armed forces.” Id. § 2(c).


Section 3 of the WPR, which requires the President to consult Congress before introducing forces into “hostilities” or “situations where imminent involvement in hostilities is clearly indicated by the circumstances,” is also intended to ensure congressional knowledge and input prior to engagements of U.S. armed forces abroad. Id. § 3.


Id. § 4(a). The limited exceptions for reporting combat-equipped deployments are for those “which relate solely to supply, replacement, repair, or training of such forces.” Id. § 4(a)(2).


All reports under section 4(a) are required to provide, in writing: “(A) the circumstances necessitating the introduction of United States Armed Forces; (B) the constitutional and legislative authority under which such introduction took place; and (C) the estimated scope and duration of the hostilities or involvement.” Id. § 4(a). The legislative history makes clear that the WPR’s reporting provisions are intended to “ensure that the Congress by right and as a matter of law will be provided with all the information it requires to carry out its constitutional responsibilities with respect to committing the Nation to war and to the use of United States Armed Forces abroad.” H.R. Rep. No. 93-547, at 8 (1973) (Conf. Rep.).


Section 5(b) of the WPR provides that 60 days after a report under section 4(a)(1) is “required to be submitted,” the President “shall terminate any use of United States Armed Forces with respect to which such report was submitted (or required to be submitted)” unless Congress has authorized such use of U.S. Armed Forces during that period. War Powers Resolution § 5(b). Termination is not required, however, if Congress has extended the period “by law” or “is physically unable to meet as a result of an armed attack on the United States.” Id. The 60-day period may be extended to “not more than” 90 days if the President “certifies to the Congress in writing that unavoidable military necessity respecting the safety of United States Armed Forces requires the continued use of such armed forces in the course of bringing about a prompt removal of such forces.” Id. A separate provision, section 5(c), requires the President to remove armed forces “engaged in hostilities” outside the United States at any time “if the Congress so directs by concurrent resolution.” Id. § 5(c). This provision was subsequently gutted by an unrelated Supreme Court decision. See infra note 16.


In 1975, the Ford Administration described “hostilities” as “a situation in which units of U.S. armed forces are actively engaged in exchanges of fire with opposing units of hostile forces.” Letter from Monroe Leigh, Legal Adviser, U.S. Dep’t of State, and Martin R. Hoffman, Gen. Counsel, U.S. Dep’t of Def., to Hon. Clement J. Zablocki, Chairman, Subcomm. on Int’l Sec. and Sci. Affairs, Comm. on Int’l Relations, U.S. House of Representatives (June 3, 1975), in War Powers: A Test of Compliance: Hearings Before the Subcomm. on Int’l Sec. and Sci. Affairs of the House Comm. on Int’l Relations, 94th Cong. 38–40 (1975). See generally Libya and War Powers: Hearing Before the S. Foreign Relations Comm., 112th Cong. (2011) [hereinafter Koh Hearing] (statement of Harold Hongju Koh, Legal Adviser, U.S. Dep’t of State), (arguing that historical practice suggests that situations in which the nature of the mission, exposure of U.S. armed forces, risk of escalation, and military means are limited do not constitute “hostilities” that trigger the WPR’s 60-day automatic pullout provision); Deployment of United States Armed Forces to Haiti, 28 Op. O.L.C. 30, 34 (2004), (“Although it is also possible that some level of violence and instability will continue, we previously have concluded that ‘the term “hostilities” should not be read necessarily to include sporadic military or paramilitary attacks on our armed forces.’” (quoting Presidential Power to Use Armed Forces Abroad Without Statutory Authorization, 4A Op. O.L.C. 185, 194 (1980))); Overview of the War Powers Resolution, 8 Op. O.L.C. 271, 275 (1984), (“The Ford Administration took the position that ‘hostilities’ meant a situation in which units of our armed forces are ‘actively engaged in exchanges of fire’” and “‘imminent hostilities’ meant a situation in which there is a ‘serious risk’ from hostile fire to the safety of United States Armed Forces. ‘In our view, neither term necessarily encompasses irregular or infrequent violence which may occur in a particular area.’” (citing War Powers: A Test of Compliance, supra)).


See Letter from Richard Nixon, President of the U.S., to the House of Representatives on Veto of the War Powers Resolution (Oct. 24, 1973) (arguing that the termination provision is unconstitutional because it “would allow the Congress to eliminate certain authorities merely by the passage of a concurrent resolution—an action which does not normally have the force of law, since it denies the President his constitutional role in approving legislation”).


See Immigration and Naturalization Service v. Chadha, 462 U.S. 919 (1983). As Bridgeman and Pomper explain, the decision, “by invalidating the ‘legislative veto,’ casts essentially fatal doubt on Congress’ ability to order the withdrawal of U.S. forces by concurrent resolution. Following Chadha, in the face of presidential resistance, Congress can only enforce withdrawal if it commands a veto-proof supermajority. The Supreme Court’s decision also encouraged a lingering (and in our view incorrect) impression that other provisions of the War Powers Resolution are constitutionally infirm — an impression that the executive branch has sometimes encouraged.” Bridgeman and Pomper, supra note 4.


See Nixon, supra note 15 (stating that the WPR “would attempt to take away, by a mere legislative act, authorities which the President has properly exercised under the Constitution for almost 200 years. One of its provisions would automatically cut off certain authorities after sixty days unless the Congress extended them” and arguing that this provision is “unconstitutional”).


Presidential Power to Use the Armed Forces Abroad Without Statutory Authorization, 4A Op. O.L.C. at 196; see also Koh Hearing, supra note 14 (“The Administration recognizes that Congress has powers to regulate and terminate uses of force, and that the War Powers Resolution plays an important role in promoting interbranch dialogue and deliberation on these critical matters.”); Authorization for Continuing Hostilities in Kosovo, 24 Op. O.L.C. 327 (2000),


As a 1979 O.L.C. opinion explains, “When President Nixon vetoed the Resolution he did not suggest that either the reporting or consultation requirements were unconstitutional. Neither the Ford nor Carter administrations have taken the position that these requirements are unconstitutional on their face.” Supplementary Discussion of the President’s Powers Relating to the Seizure of the American Embassy in Iran, 4A Op. O.L.C. 123, 128 (1979), It then explains that “[t]he only provision that this Administration has suggested presents constitutional problems related to the right of Congress to act by concurrent resolution,” while noting some potential applications in which the consultation requirements—but not the reporting requirements—could “raise constitutional questions.” Id. at 128–29, 128 n.4 (internal citations omitted). It should be noted that Presidents often state they are providing reports “consistent with” the WPR, rather than “pursuant to” its requirements, in what could be seen as an attempt to preserve an argument that the reporting may not be required. However, this has not been a meaningful distinction in practice and the reporting requirements have not in fact been contested.


President W. Bush also only filed eight reports in his first term, but two of them reported the beginning of major combat operations in large-scale, long-term armed conflicts—the conflict against al-Qaida and the Taliban in Afghanistan that quickly metastasized into the “Global War on Terror,” and the 2003 invasion of Iraq. See George W. Bush, Report on Military Actions Taken to Respond to the Threat of Terrorism, H.R. Doc. No. 107-131 (Oct. 9, 2001); George W. Bush, A Report Consistent with the War Powers Resolution Regarding the Use of Military Force Against Iraq, H.R. Doc. No. 108-54 (Mar. 21, 2003).


Note that this adds up to more than 105 because some reports were coded as having more than one trigger under section 4(a) of the WPR.


For example, President H.W. Bush reported on August 6, 1990, a deployment to “provide additional security at the U.S. Embassy in Monrovia, Liberia” and “extract American citizens . . . . and a limited number of foreign nationals,” and stated that the mission is “not intended to alter or preserve the existing political status quo or to make the U.S. presence felt in any way.See Letter from George H.W. Bush, President of the U.S., to Congressional Leaders on the Use of United States Armed Forces in Liberia (Aug. 6, 1990) (emphasis added). Similarly, President Clinton reported on March 27, 1997, deployment of a “standby evacuation force” to provide security for U.S. citizens and “selected third country nationals” in Kinshasa, Democratic Republic of the Congo (formerly Zaire), and stated that “this movement is being undertaken solely for the purpose of preparing to protect American citizens and property.” See Letter from William J. Clinton, President of the U.S., to Congressional Leaders on the Situation in Zaire (Mar. 27, 1997) (emphasis added).


Only one report was categorized as “other”—President Obama’s report on October 14, 2015, which stated the purpose of a combat-equipped introduction of forces into Chad only as “to conduct airborne intelligence, surveillance, and reconnaissance operations in the region.” See Letter from Barack Obama, President of the U.S., to Congressional Leaders on the Deployment of United States Armed Forces Personnel to Cameroon (Oct. 14, 2015).


The only outlier is the Obama Administration’s October 14, 2016, report notifying Congress of air strikes “in response to anti-ship cruise missile launches perpetrated by Houthi insurgents that threatened U.S. Navy warships in the international waters of the Red Sea.” Letter from Barack Obama, President of the U.S., to Congressional Leaders on the War Powers Resolution Report for Yemen (Oct. 14, 2016).


Whether all of this activity should properly be understood as falling under the 2001 AUMF remains a matter of debate.


The January 18, 1991, report states that combat operations to “compel Iraq to withdraw unconditionally from Kuwait and meet the other requirements of the U.N. Security Council and the world community” were taken both “pursuant to my authority as Commander in Chief” and as “contemplated by . . . H.J. Res. 77, adopted by Congress on January 12, 1991.” Letter from George H.W. Bush, President of the U.S., to Congressional Leaders on the Persian Gulf Conflict (Jan. 18, 1991).


The March 21, 2003, report states that “combat operations . . . against Iraq” were undertaken “pursuant to my authority as Commander in Chief and consistent with the Authorization for Use of Military Force Against Iraq Resolution (Public Law 102–1) and the Authorization for Use of Military Force Against Iraq Resolution of 2002 (Public Law 107–243).” George W. Bush, A Report Consistent with the War Powers Resolution Regarding the Use of Military Force Against Iraq, H.R. Doc. No. 108-54 (Mar. 21, 2003).


While it does not explicitly claim the 2001 AUMF as a source of authority for the reported operations, President W. Bush’s Sept. 24, 2001, report subsequently notes the 2001 AUMF, alongside the WPR, as follows:

I am providing this report as part of my efforts to keep the Congress informed, consistent with the War Powers Resolution and Senate Joint Resolution 23, which I signed on September 18, 2001. As you know, officials of my Administration and I have been regularly communicating with the leadership and other Members of Congress about the actions we are taking to respond to the threat of terrorism and we will continue to do so. I appreciate the continuing support of the Congress, including its passage of Senate Joint Resolution 23, in this action to protect the security of the United States of America and its citizens, civilian and military, here and abroad.

Letter from George W. Bush, President of the U.S., to Congressional Leaders on the Deployment of Forces in Response to the Terrorist Attacks of September 11 (Sept. 24, 2001).


President Reagan’s March 19, 1982, report states: “The deployment of U.S. forces to the Sinai for this purpose is being undertaken pursuant to Public Law 97-132 of December 29, 1981, and pursuant to the President’s constitutional authority with respect to the conduct of foreign relations and as Commander-in-Chief of U.S. Armed Forces.” Letter from Ronald Reagan, President of the U.S., to Congressional Leaders on United States Participation in the Multinational Force and Observers (Mar. 19, 1982).


One of the stated purposes of the WPR is “to fulfill the intent of the framers of the Constitution of the United States and insure that the collective judgement of both the Congress and the President will apply to the introduction of United States Armed Forces into hostilities . . . .” War Powers Resolution, Pub. L. No. 93-148, § 2(a), 87 Stat. 555, 555 (1973).


For example, the invasion of Iraq in 2003 arguably was not a response to an imminent threat of attack against the United States.


Some forms of international support, most notably a strong UN Security Council mandate, can also be seen as bolstering domestic legal authority for presidential action.


Under the WPR, the 60-day clock is only triggered by an introduction into hostilities or imminent involvement in hostilities that is clearly indicated by the circumstances. See War Powers Resolution § 4(a)(1); see also supra note 13.


See supra note 14.


Note that this dataset records each of these six instances as triggered by section 4(a)(1).


Marty Lederman, for example, argues:

It is possible, but uncertain, that a similar interpretation was at work with respect to the deployment of U.S. aircraft to Bosnia in support of a NATO-enforced “no-fly” zone in 1994. In that case, President Clinton reported to Congress in March and April 1994 that U.S. forces had fired against Serbian forces. There was no withdrawal of U.S. forces 60 days after either WPR report; and then in August and again in November of that year, President Clinton filed separate WPR reports of additional U.S. strikes against Serbian forces, thereby suggesting (without stating) that the Administration might have concluded that “hostilities” and a “clear indication” of “imminent hostilities” had perhaps terminated sometime after each discrete operation, and that a new 60-day clock began running upon each resumption of active engagement with or against the Serbs.

Marty Lederman, The War Powers Clock(s) in Iraq, Just Security (Sept. 8, 2014),


War Powers Resolution, Pub. L. No. 93-148, § 4(a), 87 Stat. 555, 555–56 (1973).


President Obama’s report on October 14, 2015, stated the purpose of a combat-equipped introduction of forces into Chad only as “to conduct airborne intelligence, surveillance, and reconnaissance [ISR] operations in the region.” Letter from Barack Obama to Congressional Leaders (Oct. 14, 2015), supra note 39. While this provides some information as to the purpose of the deployment, the nature of the ISR mission is not provided.


Both of these are reports by President H.W. Bush in 1990: one regarding an embassy protection mission in Liberia, see Letter from George H.W. Bush to Congressional Leaders (Aug. 6, 1990), supra note 38, and the other reporting the build-up of forces in the Persian Gulf region in 1990 prior to the Gulf War, see Letter from George H.W. Bush, President of the U.S., to Congressional Leaders on the Deployment of Additional United States Armed Forces to the Persian Gulf (Nov. 16, 1990). The reason for this deficiency is unclear. Given that President H.W. Bush’s other reports do cite domestic authority, this could be a simple oversight on the part of those preparing the two reports at issue.


This language, used by President Reagan in a September 29, 1982, report, was echoed in substance in dozens of reports to follow by his and other administrations. See Letter from Ronald Reagan, President of the U.S., to Congressional Leaders on United States Participation in the Multinational Force in Lebanon (Sept. 29, 1982).


For this reason, a coding category was developed that would be applicable to reports that did not provide a specific estimated duration, but nevertheless attempted to describe this information based on the objectives of or need for the mission (coded as “mission-bound but unspecified”).


War Powers, Libya, and State-Sponsored Terrorism: Hearings Before the Subcomm. on Arms Control, Int’l Sec. and Sci. of the H. Comm. on Foreign Affairs, 99th Cong. 9 (1986) (statement of Abraham D. Sofaer, Legal Adviser, Dep’t of State) (arguing that “[w]here a peaceful operation does in fact result in hostile action to which U.S. forces must respond in immediate self-defense, such an isolated engagement should not normally be construed as constituting the introduction of U.S. Armed Forces into a situation of actual or imminent hostilities for the purpose of the reporting requirement of section 4” and noting that “[n]o report was submitted in the case of the 1981 Sidra incident, during which two Libyan aircraft were shot down after they fired at us”)).


As the CRS has noted, “[T]he United States undertook a series of exercises in Honduras that some believed might lead to conflict with Nicaragua. On March 25, 1986, unarmed U.S. military helicopters and crewmen ferried Honduran troops to the Nicaraguan border to repel Nicaraguan troops.” Torreon & Plagakis, Cong. Research Serv., supra note 33, at 12.


See Scott Anderson, Yemen and the Limits of Congressional War Powers, Tex. Nat’l Security Rev.: Pol’y Roundtable (Nov. 14, 2019),; Tess Bridgeman, Congress, Saudi Arabia, and the Conflict in Yemen: Where do We Go from Here?, Just Security (Feb. 12, 2019),


Additional types of information not represented in this database—and not reported under any administration to date—should arguably be incorporated to keep Congress and the American people fully informed of the consequences associated with reported activity. These might include, for example, the estimated financial costs of the reported operation and an assessment of the specific goals or benchmarks that would indicate mission success.


Researchers primarily used “Appendix A: Instances Reported under the War Powers Resolution” of the Congressional Research Service (CRS) Report titled “The War Powers Resolution: Concepts and Practice” to identify these reports, in addition to the current White House website and White House website archives, congressional records, and other sources. See Weed, Cong. Research Serv., supra note 6, at app. A.


Periodic (or “supplemental”) reports provided to Congress pursuant to section 4(c) of the WPR are excluded from this dataset. These reports, which the President must periodically provide to Congress on ongoing activities that have already been reported in a previous 48-hour report, serve a different purpose than 48-hour reports and cannot be analyzed subject to the same criteria. They are nevertheless an important supplemental source of information about the scope of deployments and operations notified in the 48-hour reports collected and analyzed here. Section 4(c) of the WPR requires that “the President shall, so long as [U.S.] armed forces continue to be engaged in such hostilities or situation, report to the Congress periodically on the status of such hostilities or situation as well as on the scope and duration of such hostilities or situation, but in no event shall he report to the Congress less often than once every six months.” War Powers Resolution, Pub. L. No. 93-148, § 4(c), 87 Stat. 555, 556 (1973).


See, e.g., Letter from Donald J. Trump, President of the U.S., to Congressional Leaders on the Global Deployment of United States Combat-Equipped Armed Forces (Dec. 7, 2018),; Letter from Barack Obama, President of the U.S., to Congressional Leaders on the Global Deployments of United States Combat-Equipped Armed Forces (June 12, 2014),


At least one fully classified 48-hour report is known to exist. President Trump submitted a classified 48-hour report to Congress on January 4, 2020, relating to a U.S. drone strike killing Iranian General Qassem Soleimani (and Iraqi military personnel) in Baghdad, Iraq, on January 2, 2020. See Press Release, Nancy Pelosi, Speaker of the House, Pelosi Statement on White House’s War Powers Act Notification of Hostilities Against Iran (Jan. 4, 2020), The WPR does not state that reports must be unclassified. Nevertheless, classified WPR reporting is controversial. On one hand, it undermines the crucial transparency function provided by the 48-hour reporting requirement, eliminating the possibility that the public will have an opportunity to engage its elected representatives on the reported activity. It also makes it harder for members of Congress to access and discuss the information, as they may only do so in specified, secure facilities and have a limited number of aides (if any) who may also access the information. On the other hand, another key purpose of the WPR’s reporting requirements is to ensure Congress has as much information as possible about the President’s use of armed forces abroad—should some of this information necessarily remain classified, it would be a perverse result if such information were withheld from Congress out of a perceived mandate to ensure all WPR-reporting is unclassified.


See, e.g., supra note 14 and accompanying text.


Categories for which additional unstructured data were recorded include the stated purpose or mission, the type of military activity, the constitutional or legislative authority, the estimated scope and duration of the activity, other 48-hour reports that are related to the report at issue, the international legal basis for the action if noted, U.S. or non-U.S. casualties if noted, and reported information regarding coalition or joint missions.


Weed, Cong. Research Serv., supra note 6, at 53 (quoting H.R. Rep. No. 93-287, at 7 (1973)).


The “combat-equipped introduction” and “substantial enlargement” prongs are in most instances, but not always, mutually exclusive. This is because either a combat-equipped contingent is not yet present in the country at issue, in which case a report describing the introduction of such forces was triggered by section 4(a)(2), or additional combat-equipped personnel are being introduced in numbers that substantially enlarge the existing presence, in which case the section 4(a)(3) prong was triggered. However, there are a few instances in which Presidents describe within a single report the deployment of combat-equipped forces to more than one location. In two of these instances, the report was coded as triggered by both an initial “combat-equipped introduction” under section 4(a)(2) and a substantial enlargement (in a different location) under section 4(a)(3). See Letter from William J. Clinton, President of the U.S., to Congressional Leaders on Airstrikes Against Serbian Targets in the Federal Republic of Yugoslavia (Serbia and Montenegro) (Apr. 7, 1999) (reporting deployments to Albania and Macedonia); Letter from William J. Clinton, President of the U.S., to Congressional Leaders on Bosnia (Dec. 6, 1995) (reporting deployments to Bosnia and Herzegovina, Croatia, Hungary, and Italy).


Aside from required periodic reporting, a new 48-hour report could be required in three primary circumstances: (1) a substantial enlargement of a combat-equipped deployment; (2) a new episode of hostilities after the initially reported hostilities cease; or (3) an episode of hostilities or a change in circumstances clearly indicating imminent involvement in hostilities following a report based on the combat-equipped or substantial enlargement prongs. Whether reporting is required under the third scenario remains contested.


Authorization for Use of Military Force Against Iraq Resolution of 2002, Pub. L. No. 107-243, 116 Stat. 1498 (2002).


Authorization for Use of Military Force, Pub. L. No. 107-40, 115 Stat. 224 (2001).


Section 4(a) requires 48-hour reporting “[i]n the absence of a declaration of war.” War Powers Resolution, Pub. L. No. 93-148, § 4(a), 87 Stat. 555, 555–56 (1973). This carve-out for declared wars has been interpreted to encompass an implicit exception to WPR reporting for other authorized uses of force. See, e.g., Weed, Cong. Research Serv., supra note 6, at 2 (“Section 4(a)(1) requires reporting within 48 hours, in the absence of a declaration of war or congressional authorization . . . .” (emphasis added)). Nevertheless, as discussed further below, Presidents have reported statutorily authorized activity at the outset of major deployments or combat operations abroad.


This interpretation, while now long-held, was not settled in the first decade after the WPR’s passage. See The Iranian Hostage Crisis, Introduction and Summary, 4A Op. O.L.C. 88 n.18 (1980), (“The February 12, 1980, opinion also concluded, as a threshold matter, that the term ‘United States Armed Forces’ in the War Powers Resolution does not include military personnel detailed to and under the control of the Central Intelligence Agency. That conclusion was expressly reconsidered and reversed by the Office of Legal Counsel in a subsequent opinion . . . entitled ‘War Powers Resolution: Detailing of Military Personnel to the CIA.’”).


See Barbara Salazar Torreon & Sofia Plagakis, Cong. Research Serv., R42738, Instances of Use of United States Armed Forces Abroad, 1798-2019 (2019); Weed, Cong. Research Serv., supra note 6, at app. B (“Instances Not Formally Reported to the Congress Under the War Powers Resolution”).


A number of the categories of data do not apply to unreported activity because they analyze aspects of the reporting itself, and thus were coded as “not applicable.” For example, there can be no “estimated scope and duration” when there is no WPR report. Researchers did, however, attempt to categorize key data, such as the purpose or mission of the activity, the type of military activity, whether the mission appeared to be unilateral or involve coalition or joint forces, and other substantive information that can be inferred both from the CRS reports and limited additional research into the unreported activity at issue (such as examining contemporaneous newspaper articles or press releases).