Common Interpretation

Declare War Clause


The Constitution’s Article I, Section 8 specifically lists as a power of Congress the power “to declare War,” which unquestionably gives the legislature the power to initiate hostilities. The extent to which this clause limits the President’s ability to use military force without Congress’s affirmative approval remains highly contested.

Most people agree, at minimum, that the Declare War Clause grants Congress an exclusive power. That is, Presidents cannot, on their own authority, declare war. Although it is somewhat more contested among scholars and commentators, most people also agree that Presidents cannot initiate wars on their own authority (a minority argues that Presidents may initiate uses of force without formally declaring war and that  Congress’s exclusive power to “declare war” refers only to issuing a formal proclamation).

In the early post-ratification period, the clause’s limit on presidential warmaking was read broadly. Many key founders, including Alexander Hamilton, George Washington and James Madison, referred to the clause’s importance as a limit on presidential power. In the nation’s early conflicts, Congress’s approval was thought necessary – not only for the War of 1812, for which Congress issued a formal declaration, but also for lesser uses of force including the Quasi-War with France in 1798, conflicts with the Barbary States of Tripoli and Algiers, and conflicts with Native American tribes on the Western frontier (all of which were approved by Congress, albeit without formal declarations).

In modern times, however, Presidents have used military force without formal declarations or express consent from Congress on multiple occasions. For example, President Truman ordered U.S. forces into combat in Korea; President Reagan ordered the use of military force in, among other places, Libya, Grenada and Lebanon; President George H.W. Bush directed an invasion of Panama to topple the government of Manual Noriega; and President Obama used air strikes to support the ouster of Muammar Qaddafi in Libya. Some commentators argue that, whatever the original meaning of the Declare War Clause, these episodes (among others) establish a modern practice that allows the President considerable independent power to use military force.

In general, most scholars and commentators accept that presidential uses of force comport with the Declare War Clause if they come within one of three (or possibly four) categories, though the scope of these categories remains contested. First, Presidents may use military force if specifically authorized by Congress. Authorization may come from a formal declaration of war, but it can also come from a more informal statutory authorization. For example, after the September 11, 2001 attacks, Congress authorized the President to use force against those who launched the attacks and those who supported or assisted them. Sometimes, authorizations are fairly specific (as when Congress authorized President George W. Bush to use force against Iraq); sometimes they are more open-ended, as when Congress authorized the use of force to protect U.S. interests and allies in Southeast Asia, leading to the Vietnam War. Most people agree that presidential actions pursuant to such authorizations are constitutional, although there may be debate about how broadly to read any particular authorization. More controversially, Presidents have claimed authorization from informal or indirect congressional actions, such as approval of military spending, assent by congressional leaders, or even Congress’s failure to object to ongoing hostilities.

Second, Presidents are thought to have independent authority to use military force in response to attacks on the United States. At the 1787 Philadelphia convention, Madison described the Declare War Clause as leaving the President with authority to repel sudden attacks. The scope of this power is sharply contested, however. Some commentators think it includes defense against attacks on U.S. citizens or forces abroad, in addition to attacks on U.S. territory; some would extend it to attacks on U.S. allies or U.S. interests, defined broadly. Some commentators think it includes defense against threats as well as actual attacks. Some think it allows the President not only to take defensive measures but also to use offensive force against attackers.

Third, Presidents may use other constitutional powers – principally the commander-in-chief power – to deploy U.S. forces in situations that do not amount to war. For example, President Bush’s deployment of troops to Saudi Arabia after Iraq’s invasion of Kuwait in 1990 probably did not implicate the declare war clause because at that point the troops were not involved in combat. Similarly, deployment of U.S. troops as peacekeepers (as President Clinton did in Bosnia) likely does not involve the United States in war and thus does not require Congress’s approval under the Declare War Clause. More controversially, it is claimed that involvement in low-level hostilities may not rise to the level of war in the constitutional sense. President Obama argued on this ground that U.S. participation in the bombing campaign in Libya in 2011 did not require Congress’s authorization. However, this position is strongly disputed by other commentators. A related argument, also controversial, is that using force against non-state actors such as terrorist organizations does not amount to war, and thus does not implicate the Declare War Clause.

A fourth potential category is using force under the authority of the United Nations, which some commentators have argued can substitute for approval by Congress. Among other things, President Truman argued that his use of force in Korea was a “police action” to enforce the UN Charter, not a war. However, Presidents have generally not relied on this source of authority and it is less well accepted, even in theory, than the prior categories.

The law of the Declare War Clause is unsettled in part because there have been very few judicial decisions interpreting it. In the Prize Cases in 1863, the Supreme Court upheld as a defensive measure President Lincoln’s blockade of the southern states following their attack on Fort Sumter, but was ambiguous as to whether the authority for the blockade came from Article II, from specific statutes Congress had passed in 1795 and 1807, or some combination of both. And in dicta, the Court noted that the President could not begin hostilities without Congress’s approval. Earlier cases, such as Bas v. Tingy (1800), referred generally to Congress’s broad powers over warmaking without giving specific guidance on the President’s power. But in modern times, courts have generally avoided deciding war-initiation cases on the merits, based on rules that limit what types of disputes courts can resolve, such as standing or the political question doctrine. As a result, the precise contours and implications of the Declare War Clause remain unresolved today—leaving resolution of disputes over particular uses of force by the President to the political process.

Matters of Debate

The Textual Limit on the President’s War Powers


Despite widespread consensus that the Declare War Clause limits the President’s power to initiate the use of military force, it is not obvious how that limit arises from the Constitution’s text. The most common meaning of “to declare war” is to issue a formal statement called a Declaration of War that announces the new hostile relationship. Modern hostilities typically do not begin with such a statement. It is often said that the United States has fought only five “declared” wars (the War of 1812, the Mexican War, the Spanish-American War, World War I, and World War II). Others, such as the Vietnam War, are called “undeclared wars” because no such official statement was issued.

Moreover, the Framers surely understood that a formal declaration of war was not necessary prior to beginning hostilities. Eighteenth-century conflicts commonly began without formal announcements. In The Federalist No. 25, Alexander Hamilton (in a different context) observed that the formal declaration “has of late fallen into disuse.” The United States’ principal military conflicts of the immediate post-ratification period – hostilities with the Western tribes, the 1798 naval war with France, and the conflicts with the Barbary States of Algiers and Tripoli – were fought without any formal declaration.

Thus one might think the Declare War Clause refers only to official announcements of war, leaving the President with broad power to initiate “undeclared” hostilities under the executive and commander-in-chief powers. Congress could check presidential hostilities through its appropriations power, but the Declare War Clause would not have the significance often attributed to it. In modern scholarship and commentary, this is a minority view, most prominently associated with Professor John Yoo.

The narrow view of the Declare War Clause has its own difficulties, however. To begin, it is unclear why the framers would have given Congress only the narrow power to communicate about war, as the President generally is the nation’s voice in foreign affairs. Further, leading framers seemed to identify the clause as a key check on the President (which, under the narrow view, it would not be). Hamilton, for example, wrote in his first Pacificus essay (1793) that “[t]he legislature alone” can “plac[e] the nation in a state of war.” In the early post-ratification conflicts mentioned above, it was assumed that the President could not initiate hostilities without Congress’s approval, even though the conflicts were not formally declared.

Another Perspective

This essay is part of a discussion about the Declare War Clause with Stephen I. Vladeck, Professor of Law, American University Washington College of Law. Read the full discussion here.

The solution appears to be that by “declare war” the framers meant something broader than just formal declarations.  In the late seventeenth century, John Locke’s famous Second Treatise of Government referred to “declaring” hostile intent “by word or action.” Leading eighteenth-century writers such as Blackstone and Vattel used “declare” in a way that encompassed hostile actions as well as formal statements. Vattel, for example, wrote in The Law of Nations (1758) that “when one nation takes up arms against another, she from that moment declares herself an enemy to all individuals of the latter.” And, as Professor Saikrishna Prakash has demonstrated, eighteenth-century diplomatic and personal correspondence commonly referred to wars “declared” by hostile action. Thus the clause most likely referred to wars “declared” by attacks as well as by formal announcements.

This reading of the clause resolves the difficulties suggested above. Giving Congress the power to declare wars by word or action makes sense in the context of founding-era fears that the President would involve the nation in needless conflicts. It further explains why leading framers described the clause as an important limit on presidential war-initiation and why in post-ratification conflicts the President was understood to be so limited.

This reading also confirms a number of situations in which independent presidential actions are thought to be constitutionally permitted. The President (without Congress’s approval) cannot take actions that put the United States in a state of war – most obviously, military attacks on a foreign nation. But the clause does not bar presidential actions that do not put the United States in a state of war. Thus, for example, peacekeeping deployments and defensive deployments do not create a state of war. Similarly, rescue missions and other acts to protect U.S. citizens abroad may not create a state of war if they do not involve direct confrontation with foreign governments. It is important to note, however, that the eighteenth-century definition of “war” included low-level hostilities as well as total or full-scale conflict. Samuel Johnson’s 1755 dictionary defined war as “the exercise of violence under sovereign command.” Thus, limited hostilities with foreign nations, even if the United States is not fully engaged, would seem to require Congress’s approval.

More controversially, this reading of the Declare War Clause may allow the President considerable independent power to respond when foreign nations attack the United States. In that situation, a state of war already exists by the acts of the other side. Thus defensive responses – and perhaps even counterattacks – would not declare (initiate) war, and so would be within the President’s independent power. In 1801, Hamilton made this argument regarding the Tripoli conflict. While generally agreeing that the President could not initiate hostilities, Hamilton said that the Declare War Clause did not prevent the President from responding (including with offensive force) once Tripoli began the war. Modern commentary generally accepts this explanation of the President’s power to use defensive force in response to attacks, although it is debated whether the power goes as far as Hamilton said it did.

In sum, the best textual and historical account of the Declare War Clause is that it gives Congress exclusive power over both declaring war formally (in an official declaration of war) and declaring war informally (by authorizing hostile attacks). In its constitutional context, to “declare war” means to “initiate war.” Looking at the clause this way explains the framers’ assumption that the clause was an important limit on the President. It also suggests various situations in which the President can direct the military without specific congressional approval, because the clause is not violated when the President’s actions do not initiate war.

Matters of Debate

Congress’s Statutory Abdication of its Declare War Power


As Professor Ramsey cogently explains in his essay, the Declare War Clause “is not violated when the President’s actions do not initiate war.” It is also not violated when the Executive Branch uses military force (of whatever intensity) pursuant to statutory authorization; in such circumstances, the President is only carrying out authority Congress delegated pursuant to the Declare War Clause and its other war powers. That is why there is little contemporary controversy over the scope of the Declare War Clause — or its role in the separation of war powers between Congress and the Executive Branch.

Instead, most contemporary disputes between Congress and the Executive Branch over the war powers have reduced to debates over the scope of statutory authorizations that Congress has provided. And although Congress enacted the War Powers Resolution (WPR) in 1973 in an attempt to mitigate such disputes, it has thus far only served to exacerbate them, raising the question of whether there are better ways to protect the original understanding going forward.

I. Vietnam and the WPR

The War Powers Resolution was a direct response to U.S. involvement in Vietnam, which Congress initially authorized in the 1964 Gulf of Tonkin Resolution. But the scale and scope of the Vietnam conflict expanded dramatically beyond what Congress could have anticipated — with the only subsequent legislative support for the conflict coming through appropriations bills. To stem the perceived rising tide of unilateral presidential warmaking, the WPR created a framework that requires the President to report to Congress within 48 hours in any case in which U.S. armed forces are introduced “into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances,” into the territory of a foreign nation for purposes other than training or supply; or “in numbers which substantially enlarge United States Armed Forces equipped for combat already located in a foreign nation.”

That report, in turn, triggers a 60-day clock (which can be extended by the President to 90 days, but no further), at the end of which the President must terminate such use of U.S. armed forces unless Congress has provided specific authorization, has extended the clock, or is unable to assemble because of an armed attack on the United States. And even before the clock has expired, the WPR gives Congress the power to terminate such uses of force pursuant to a concurrent resolution (a provision that may be unconstitutional in light of the Supreme Court’s 1983 decision in INS v. Chadha).

II. Problems With the WPR

Although the WPR was meant to cabin unilateral presidential warmaking and reassert Congress’s constitutional prerogative in the field, practice (and most academic commentary) to date suggests that it has been a spectacular failure.

First, the statutory framework does not kick in until the “clock” starts, which itself turns on when the President actually submits the report to Congress required by the statute, or when he was “required to,” whichever comes first. In practice, Congress has been reluctant to decide for itself when the clock starts, which has left the Executive Branch with at least some discretion to slow-walk the report (or not file one at all) in order to buy more time for unilateral uses of force.

Another Perspective

This essay is part of a discussion about the Declare War Clause with Michael D. Ramsey, Hugh and Hazel Darling Foundation Professor of Law and Director, International & Comparative Law Programs, University of San Diego School of Law. Read the full discussion here.

Second, and related, the WPR clock turns on the existence of “hostilities,” an “ambiguous term of art,” in the words of one Executive Branch lawyer, which has been interpreted narrowly to avoid triggering the WPR framework. Thus, President Obama defended the continuing use of military force in Libya after the WPR clock expired in April 2011 on the ground that it did not constitute “hostilities,” since it was a limited mission, with limited exposure for U.S. armed forces, with very little risk of escalation, and using limited military means. The more narrowly “hostilities” can be interpreted in this manner, the more force future Presidents can engage in unilaterally without even triggering the WPR.

Third, although the WPR was meant to limit presidential warmaking, its framework all-but appears to embrace it in the short term, at least until its clock runs out. After all, by providing for the termination of military force at the end of the statutory time-period, the WPR implicitly appears to authorize such force until the termination provisions kick in, creating 60-to-90 days of authority that Congress might not otherwise have provided.

Fourth, and perhaps most significantly, the WPR says nothing about how to interpret the specific statutory authorizations that satisfy it, such as the Authorization for the Use of Military Force (AUMF) Congress enacted shortly after the September 11 attacks. Congress intended the AUMF to authorize the use of military force against those groups that were directly responsible for the September 11 attacks, but Presidents Bush and Obama subsequently interpreted its broad language to authorize force against an ever-widening array of “associated forces” of such groups, and against individuals (and in countries) with little or no connection to 9/11. The lack of specificity in the AUMF became especially apparent when the Obama administration argued that it authorized hostilities against the Islamic State in Iraq and the Levant (ISIL), a group that did not even exist on September 11 — and that was quite publicly at odds with al Qaeda, the principal perpetrators of those attacks. Whether such a reading of the AUMF was valid or not did not in any way depend upon the WPR.

III. The Future of War Powers

As a result, it seems unlikely that the War Powers Resolution will serve any salutary purpose in separating the war powers between Congress and the President going forward or in vindicating the original understanding of the Declare War Clause. And, as the AUMF debate underscores, not only will Presidents interpret statutory authorizations broadly, but Congress will be reluctant to seek their repeal. Instead, to protect the original understanding of Congress’s central institutional role in authorizing offensive uses of military force, what is needed is not another framework statute like the WPR, but rather a commitment from Congress to avoid open-ended use-of-force authorizations like the AUMF — or, at the very least, to enact them with sunsets, so that the legislature is forced to revisit such authorizations on a regular basis, and must then affirmatively undertake to reenact them, rather than repeal them.

Matters of Debate

More about Article I

The Drafting Table

Explore key historical documents that inspired the Framers of the Constitution and each amendment during the drafting process, the early drafts and major proposals behind each provision, and discover how the drafters deliberated, agreed and disagreed, on the path to compromise and the final text.

In the Classroom

Teach the Constitution in your classroom with nonpartisan resources including videos, lesson plans, podcasts, and more. Check out our classroom resources organized by each article or amendment, and by key constitutional questions.

Media Library: Article I

Town Hall Video

The Girl in the Picture: Remembering Vietnam

Kim Phuc, Mark Bowden, and Hannibal Lokumbe join the NCC for a unique discussion and performance centered on the Vietnam War and…

Dec 6

Blog Post

The Gulf of Tonkin Resolution and the limits of presidential power

It was on this day in 1964 that a joint session of Congress approved the Gulf of Tonkin Resolution, an act that led to the Vietnam…

Aug 7

More from the National Constitution Center

Carry the Constitution in Your Pocket! Download the App

The Interactive Constitution is available as a free app on your mobile device.

Visit the National Constitution Center

Find out about upcoming programs, exhibits, and educational initiatives on the National Constitution Center’s website.

Support the Interactive Constitution

The National Constitution is a private nonprofit. Please support our educational mission of increasing awareness and understanding of the U.S. Constitution.