The Declare War Clause, Part 8: Vietnam War Through 21st-Century Conflicts

Legal Sidebari

The Declare War Clause, Part 8: Vietnam War

Through 21st-Century Conflicts

September 30, 2024

This Legal Sidebar is the last in an eight-part series that discusses the Declare War Clause in Article I,

Section 8, Clause 11 of the Constitution, which grants Congress the power “To declare War, grant Letters

of Marque and Reprisal, and make Rules concerning Captures on Land and Water[.]” The power to take

the nation to war is a central element of the Constitution’s scheme of war powers, but interpretation of the

Declare War Clause is complex and evolving. This Sidebar series discusses the Supreme Court’s

jurisprudence related to declarations of war by Congress and highlights interbranch practices that

illuminate the executive and legislative branches’ sometimes differing interpretations of the clause. This

Sidebar examines the President’s authority to take military action absent a declaration of war or clear

statutory authorization from Congress. Additional information on Congress’s war powers and the

President’s powers as Commander-in-Chief can be found in the Constitution Annotated.

The Vietnam War

After North Vietnamese patrol boats reportedly attacked U.S. naval vessels in international waters in

Southeast Asia, Congress enacted a joint resolution, known as the Gulf of Tonkin Resolution, authorizing

the President to “take all necessary measures to repel any armed attack against the forces of the United

States and to prevent further aggression.” As the conflict unfolded and spread beyond Vietnam’s borders,

some Members of Congress questioned whether military operations had become so extensive that they

exceed the Gulf of Tonkin Resolution’s scope and required a declaration of war. President Lyndon

Johnson claimed the Constitution alone provided sufficient authority and would have done so even if

Congress never enacted the Gulf of Tonkin Resolution. Executive branch attorneys, on the other hand,

relied on a combination of the President’s Article II powers and the Gulf of Tonkin Resolution as

domestic legal authorities. In an executive branch legal opinion addressing the introduction of U.S. forces

into Cambodia, then-Assistant Attorney General (and later Chief Justice of the Supreme Court) William

Rehnquist took the view that the military action fell “short of war” and was “the sort of tactical decision

traditionally confided to the Commander in Chief in the conduct of armed conflict.”

In 1971, Congress passed and President Nixon signed laws repealing the Gulf of Tonkin Resolution and

calling for the “prompt and orderly” withdrawal of U.S. troops at the “earliest practicable date.” U.S.

Congressional Research Service

https://crsreports.congress.gov

LSB11237

CRS Legal Sidebar

Prepared for Members and

Committees of Congress

Congressional Research Service

2

troop presence diminished considerably during this period as the Nixon Administration carried out a

policy to transfer control of the conflict to South Vietnamese forces, but the Nixon Administration

continued aerial campaigns after the Gulf of Tonkin Resolution was rescinded. Congress eventually

passed, and the President signed, legislation prohibiting use of appropriated funds for military operations

in Southeast Asia and setting a ceiling on U.S. civilian and military personnel in Vietnam. By 1973,

Congress’s dissatisfaction with presidential use of armed forces without congressional authorization or

consultation led it to enact the War Powers Resolution (discussed in detail in other CRS products) over

President Nixon’s veto.

Federal courts considered several cases contesting the constitutionality of military action in Vietnam and

Southeast Asia, but no case successfully challenged the conflict or permanently constrained presidential

action. Some lower courts held that these cases presented nonjusticiable political questions, and the

Supreme Court affirmed one district court’s dismissal of a class action challenge to the constitutionality of

the Vietnam War on that basis. Other lower courts concluded that the question of whether congressional

authorization was required for military action could be justiciable in some circumstances. These courts

either held that Congress authorized military action by appropriating funds and extending the compulsory

draft or that judicial intervention was not appropriate while the President was in the process of winding

down the conflict.

One district court issued an order, later reversed on appeal, that enjoined an air campaign in Cambodia on

the grounds that the military action exceeded the President’s authority. Following a complex set of rapidly

issued opinions during an appeals process in which Supreme Court Justices served as judges on the U.S.

Court of Appeals for the Second Circuit, the stay was implemented for less than 24 hours.

Post-Cold War Operations

After the end of the Vietnam War and enactment of the War Powers Resolution, Presidents continued to

claim constitutional authority to introduce troops in hostile circumstances without advance congressional

authorization. In the period between the close of the Vietnam War and the First Persian Gulf War,

examples include

•

•

•

•

President Ford’s evacuation of individuals from Vietnam and Cambodia despite Vietnamera appropriations restrictions;

President Carter’s order to rescue hostages held in the American Embassy in Tehran;

President Reagan’s introduction of 1,900 land forces into the Caribbean country of

Grenada to protect American citizens during a violent transition in government; and

President George H. W. Bush’s deployment of 11,000 ground forces into Panama

resulting in the arrest by U.S. forces of Panamanian leader Manuel Noriega.

After President Reagan sent a contingent of U.S. forces to Lebanon in 1982 as part of multinational

peacekeeping mission, Congress passed the Multinational Force in Lebanon Resolution, which authorized

participation in the mission, but limited that authorization for 18 months. President Reagan signed the

joint resolution, but noted in a statement that the law should not be interpreted to acknowledge that

Congress could intrude on the President’s power to use force beyond statutory timelines.

The Persian Gulf War of 1991

When a contingent of Iraqi forces entered Kuwait in 1990, the UN Security Council issued a series of

resolutions authorizing countries to take “all necessary means” to force Iraqi withdrawal. In January 1991,

Congress authorized the President to use military force to achieve the Security Council resolutions’

objectives, provided the President determined that diplomatic and other peaceful means were not

Congressional Research Service

3

successful in obtaining compliance with the Security Council’s aims. Although President George H. W.

Bush requested the congressional authorization, he and officials in his Administration also expressed the

view that the President possessed constitutional authority for the military action even if Congress had not

enacted the resolution.

The Clinton Administration

President Clinton claimed authority for several military actions overseas, including deployment of up to

20,000 troops in Haiti, multiyear military interventions with air campaigns in Bosnia and Kosovo, and a

humanitarian relief mission in Somalia. Among other legal rationales, Clinton Administration attorneys

opined that these operations were not of sufficiently significant “nature, scope, and duration” that they

interfered with Congress’s power to declare war. In some cases, the executive branch argued that

Congress provided funding or enacted other measures that authorized or contemplated military action.

Congress also exerted some influence over these missions through limitations on appropriations of funds.

For example, Congress passed, and President Clinton signed into law without constitutional objections,

legislation that set specific end dates after which funds could no longer be used to support the action and

limited the scope of some missions during this period.

September 11, 2001

Shortly after the September 11, 2001, terrorist attacks on the United States, Congress passed and

President George W. Bush signed into law a joint resolution authorizing the President to use force against

the nations, organizations, and persons the President determines were responsible for the attacks. The

Bush Administration initially requested that Congress provide broader authorization to use force “to deter

and pre-empt any future acts of terrorism or aggression against the United States[,]” but that language was

not enacted.

The Bush Administration did not view congressional authorization as necessary for its post-September 11

invasion of Afghanistan and related military actions. In late September 2001, the Office of Legal Counsel

(OLC) in the Department of Justice opined that the President already possessed independent

constitutional authority to respond to the terrorist attacks. In OLC’s view, the joint resolution “confirmed”

the President’s power, but was narrower than the constitutional authority under Article II that the

President already possessed. Although Congress declined to adopt the Bush Administration’s proposal for

a more comprehensive authorization to deter future attacks, OLC reasoned that such congressional

authorization was not legally necessary because Article II of the Constitution provided the President

plenary authority to “pre-empt . . . terrorist threats from new quarters.”

The Bush Administration OLC also opined that the Declare War Clause does not constrain presidential

power or prohibit the President from initiating a full-scale war without a declaration of war or

congressional authorization. This conclusion marked a departure from earlier OLC opinions, which

analyzed whether proposed military actions were of such a significant scale that they could rise to the

level of a war which only Congress has the power to declare. During the Obama and Trump

Administrations, OLC reverted to the executive branch’s earlier interpretation that the Declare War

Clause limits presidential power, at least in the case of a full-scale war with another country. Although

OLC withdrew some legal opinions addressing post-September 11 military actions, it has not withdrawn

the Bush Administration’s narrow interpretation of the Declare War Clause. (As discussed in other CRS

products, the Supreme Court also curtailed some of the Bush Administration’s conduct of its postSeptember 11, 2001, actions, particularly in the context of detainees and military commissions.)

Congressional Research Service

4

2003 Iraq War

After the George W. Bush Administration raised concerns over Iraq’s noncompliance with UN Security

Council resolutions and possible acquisition of weapons of mass destruction, Congress passed and

President Bush signed into law a joint resolution authorizing the President to use force to (1) defend the

United States’ national security “against the continuing threat posed by Iraq,” and (2) enforce relevant

Security Council Resolutions. While President Bush received authorization for the military action,

executive branch attorneys also took the view that such authorization was not legally necessary because

the President possessed independent constitutional authority to embark on the conflict.

Other 21st-Century Operations

In more recent decades, Presidents Obama, Trump, and Biden have each claimed independent

constitutional authority to conduct military operations without first seeking congressional approval. These

21st-century conflicts include air assault campaigns in Libya during the Obama Administration; airstrikes

against Syrian chemical weapons facilities in the Trump Administration; and air strikes targeting Iranbacked militant groups in Yemen and the Red Sea during the Biden Administration.

Author Information

Steve P. Mulligan

Attorney-Adviser

Disclaimer

This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff

to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of

Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of

information that has been provided by CRS to Members of Congress in connection with CRS’s institutional role.

CRS Reports, as a work of the United States Government, are not subject to copyright protection in the United

States. Any CRS Report may be reproduced and distributed in its entirety without permission from CRS. However,

as a CRS Report may include copyrighted images or material from a third party, you may need to obtain the

permission of the copyright holder if you wish to copy or otherwise use copyrighted material.

LSB11237 · VERSION 1 · NEW