Presidential Authority to Permit Incursion Into Communist Sanctuaries in the Cambodia-Vietnam Border Area

Presidential Authority to Permit Incursion
Into Communist Sanctuaries in the
Cambodia-Vietnam Border Area
Congress has clearly affirmed the President’s authority to take all necessary measures to protect U.S.
troops in Southeast Asia. Having determined that the incursion into the Cambodia-Vietnam border
area is such a necessary measure, the President has clear authority to order it.
The President’s action with respect to the Cambodian border area, limited in time and in geography, is
consistent with the purposes which the Executive and the Congress have pursued since 1964.
Whatever theoretical arguments might be raised with respect to the authority of the Commander in
Chief to act alone had there been no congressional sanction for our involvement in Southeast Asia,
there is no doubt as to the constitutionality of the action in light of the prior affirmance of Congress
that the Commander in Chief take all necessary measures to protect U.S. forces in Vietnam. Having
determined the necessity, the Commander in Chief has the constitutional authority to act.

May 14, 1970

MEMORANDUM OPINION FOR THE SPECIAL COUNSEL TO THE PRESIDENT*

Although the authority to declare war is vested in the Congress, the President as
Commander in Chief and sole organ of foreign affairs has constitutional authority
to engage U.S. forces in limited conflict. International law has long recognized a
distinction between formal declared wars and undeclared armed conflicts. While
the precise division of constitutional authority between President and Congress in
conflicts short of all-out war has never been formally delimited, there is no doubt
that the President with the affirmance of Congress may engage in such conflicts.
Congress has clearly affirmed the President’s authority to take all necessary
measures to protect U.S. troops in Southeast Asia. Having determined that the
incursion into the Cambodian border area is such a necessary measure, the
President has clear authority to order it.

*
Editor’s Note: This memorandum was addressed to Charles W. Colson, Special Counsel to the
President. The cover memorandum explained as follows: “Attached is a memorandum regarding the
authority of the President to permit incursion into Communist sanctuaries in the Cambodia-Vietnam
border area.” As a postscript, the cover memorandum noted: “(Copy of ‘The Legality of U.S.
Participation in the Defense of Vietnam,’ reprinted from the Department of State Bulletin, and ‘The
Legality of the United States Position in Vietnam’ by Eberhard P. Deutsch, Chairman of the American
Bar Association Committee on Peace and Law Through United Nations, also sent.)” On April 30, 1970,
two weeks before the completion of this opinion, President Nixon had announced that “a combined
American and South Vietnamese operation” would target North Vietnamese “sanctuaries on the
Cambodian-Vietnam border.” Address to the Nation on the Situation in Southeast Asia, Pub. Papers of
Pres. Richard M. Nixon 405, 407 (1970).

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I. The Commander in Chief Has Constitutional Authority to Engage
U.S. Forces in Limited Conflicts, Which Is Unquestioned
When He Has the Affirmance of Congress

A. Constitutional Authority

The constitutional provisions which relate to the use of armed force divide
authority between the Congress and the President. Congress has the authority to
provide for the common defense (art. I, § 8, cl. 1), to declare war (art. I, § 8,
cl. 11), to raise and support armies (art. I, § 8, cl. 12), to provide and maintain a
navy (art. I, § 8, cl. 13), and to make rules for governing the armed forces (art. I,
§ 8, cl. 14). The President is designated Commander in Chief of the armed forces
(art. II, § 2, cl. 1). He is vested with the “executive Power” (art. II, § 1, cl. 1) and
is charged with the duty to take care that the laws be faithfully executed (art. II,
§ 3). The nature of the executive power, as emphasized in the express authority to
make treaties, appoint ambassadors (art. II, § 2, cl. 2), and receive ambassadors
(art. II, § 3), includes the authority to conduct the nation’s foreign affairs. “The
President is the sole organ of the nation in its external relations, and its sole
representative with foreign nations.” United States v. Curtiss-Wright Exp. Corp.,
299 U.S. 304, 319 (1936) (internal quotation omitted).
This division of authority, lacking precise delimitations, was clearly intended
by the original draftsmen of the Constitution. They rejected the power of kings to
commit unwilling nations to war to further their own international political
objectives. At the same time, they recognized the need for quick executive
response to rapidly developing international situations. The accommodation of
these two interests—the prohibition of one-man commitment of a nation to war
and the need for prompt executive response to international situations—was
reflected in the Constitutional Convention’s decision to change the original
wording from the power of Congress to make war to the power to Congress to
declare war. The Founding Fathers intended to distinguish between the initiation
of armed conflict, which is for Congress to determine, and armed response to
conflict situations, which the Executive may undertake. See 3 The Papers of James
Madison 1351–53 (Henry D. Gilpin ed., 1841); 2 The Records of the Federal
Convention of 1787 318–19 (Max Farrand ed., 1966).

B. Distinction Between War and Limited Conflict

International Law has long recognized that countries engage in many forms of
armed conflict short of all-out war. These include pacific blockades or quaran-
tines, retaliatory bombardments and even sustained but limited combat. 2 Charles
Cheney Hyde, International Law: Chiefly as Interpreted and Applied by the
United States §§ 586–592 (2d rev. ed. 1945); 2 L. Oppenheim, International Law:
A Treatise §§ 26–56 (H. Lauterpacht ed., 7th ed. 1952). Early in our history, the

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Supreme Court described these differences between war and armed conflict using
the terms “solemn war” and “imperfect war”:

If it be declared in form, it is called solemn, and is of the perfect
kind; because one whole nation is at war with another whole nation;
and all the members of the nation declaring war, are authorised to
commit hostilities against all the members of the other, in every
place, and under every circumstance. In such a war all the members
act under a general authority, and all the rights and consequences of
war attach to their condition.

But hostilities may subsist between two nations more confined in
its nature and extent; being limited as to places, persons, and things;
and this is more properly termed imperfect war; because not solemn,
and because those who are authorized to commit hostilities, act
under special authority, and can go no farther than to the extent of
their commission.

Bas v. Tingy (The Eliza), 4 U.S. (4 Dall.) 37, 40 (1800) (opinion of Washington,
J.).
While the Court termed both forms of military action “war,” it marked the clear
distinction between declared war, as we have seen in this century in the two World
Wars, and undeclared armed conflicts, such as we have seen in Korea and in
Southeast Asia.

C. Historic Recognition of Distinction

As has been chronicled many times, the United States throughout its history has
been involved in armed conflicts short of all-out or declared war, from the
Undeclared War with France in 1798–1800 to Vietnam. See, e.g., H.R. Rep. No.
82-127 (1951); H.R. Doc. No. 84-443 (1956); James Grafton Rogers, World
Policing and the Constitution 92–123 (1945). The precise number of involvements
is a matter of some dispute, as is the legitimacy of them. Nevertheless they did
occur and throw considerable light on the constitutional division of powers
between the President and the Congress.
On some occasions in our history, such as the Undeclared War with France and
the Cuban Missile Crisis, Congress has, in advance, authorized military action by
the President without declaring war. Act of July 9, 1798, ch. 68, 1 Stat. 578; Pub.
L. No. 87-733, 76 Stat. 697 (1962). Chief Justice Marshall, however, raised the
question whether such authorization was necessary for the President to act with
regard to the early conflict with France:

It is by no means clear that the president of the United States
whose high duty it is to “take care that the laws be faithfully execut-

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ed,” and who is commander in chief of the armies and navies of the
United States, might not, without any special authority for that pur-
pose, in the then existing state of things, have empowered the offic-
ers commanding the armed vessels of the United States, to seize and
send into port for adjudication, American vessels which were forfeit-
ed by being engaged in this illicit commerce.

Little v. Barreme, 6 U.S. (2 Cranch) 170, 177 (1804). He held, however, where
Congress has prescribed one course of action, the President is not free to choose
another. Id. at 177–78.
There have been other times in history, such as the Mexican and Civil Wars,
where Congress has ratified armed actions, previously undertaken by the Presi-
dent. The Supreme Court has upheld the authority of the President to act prior to
the action of Congress. Citing the Mexican War as an example, Justice Grier
upheld Lincoln’s imposition of a blockade prior to the convening of Congress. The
Prize Cases, 67 U.S. (2 Black) 635, 659–60 (1863).
Frequently, Presidents have committed our armed forces to limited conflicts
without any prior approval or direct ratification by Congress. President McKin-
ley’s action in committing 5,000 troops to an international force during the Boxer
rebellion is a notable example. While Congress recognized the existence of the
conflict, as evidenced by provision for combat pay (Act of Mar. 2, 1901, ch. 803,
31 Stat. 895, 903), it did not declare war nor formally endorse the action. A federal
court, however, reiterated the early recognition of limited or undeclared war:

In the present case, at no time was there any formal declaration of
war by the political department of this government against either the
government of China or the “Boxer” element of that government. A
formal declaration of war, however, is unnecessary to constitute a
condition of war.

Hamilton v. McClaughry, 136 F. 445, 449 (C.C.D. Kan. 1905).
President Taft more than once committed American troops abroad to protect
American interests. In his annual report to Congress in 1912, he reported the
sending of some 2,000 Marines to Nicaragua and the use of warships and troops in
Cuba. H.R. Doc. No. 62-927, at 8–9, 21 (1912). He merely advised Congress of
these actions without requesting any statutory authorization. President Wilson
ordered General Pershing and more than 10,000 troops into Mexico in 1917 and
committed approximately 12,000 troops to allied actions in Russia in 1918 to
1920. No congressional action was requested or taken.
The authority of the President to commit troops in limited conflict is not, of
course, unquestioned. There are Presidents who have doubted such authority and
Congress has challenged it more than once. President Truman’s commitment of
troops in Korea in response to a United Nations (“U.N.”) resolution (S.C. Res. 83,

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U.N. Doc. S/RES/83 (June 27, 1950)) without prior approval of, or subsequent
ratification by, Congress led to the Great Debate of 1951.
President Truman had relied upon his authority as Commander in Chief and
upon resolutions of the U.N. Security Council declaring that armed aggression
existed in Korea and calling upon U.N. members to assist in halting that aggres-
sion. He cited the history of actions by the Commander in Chief to protect
American interests abroad. He characterized the U.N. Charter as the cornerstone or
our foreign relations and singled out Article 39 which authorizes the Security
Council to recommend action to members to meet armed aggression.
The President’s opponents noted that all treaties are not self-executing and that,
until implemented by Congress, non-self-executing treaties confer no new
authority on the President. Article 39, it was said, was not self-executing. Article
43, which provides expressly for the commitment of troops by members in
accordance with their constitutional processes, had been implemented to the extent
of Congress authorizing troop agreements (United Nations Participation Act of
1945, Pub. L. No. 79-264, § 6, 59 Stat. 619, 621) but since no agreements had
been entered into it was inoperative. Without any added treaty authorization, the
President’s action must be viewed solely in terms of his basic constitutional
authority, it was said, and this authority does not extend to long-term commitment
of troops in numbers ranging up to 250,000.
While various scholarly views were quoted on both sides of the issue (H.R.
Rep. No. 82-127 (1951)) and the congressional debate raged from January to
April, there was no legal resolution of the President’s authority in light of the U.N.
Charter or independent of it. Nevertheless it is clear that Congress acquiesced in
the President’s action. See David Rees, Korea: The Limited War (1964); Merlo J.
Pusey, The Way We Go To War (1969).
Since judicial precedents are virtually non-existent on this point, the question is
one which must of necessity be decided by historical practice. Viewed in this light,
congressional acquiescence in President Truman’s action furnishes strong evi-
dence that this use of his power as Commander in Chief was a proper one. This is
particularly true because, while a treaty may override a state statute under the
supremacy clause, Missouri v. Holland, 252 U.S. 416 (1920), it may not override a
specific limitation on the power of the President or of Congress, Reid v. Covert,
354 U.S. 1 (1957).

D. The Constitutional Posture Today

Under our Constitution it is clear that Congress has the sole authority to declare
formal, all-out war. It is equally clear that the President has the authority to
respond immediately to attack both at home and abroad. Between these two lies
the grey area of commitment of troops in armed conflict abroad under either
American or international auspices. In this area, both the Congress and the Presi-
dent have acted in the past. There has been dispute, often bitter, as to how far the

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President may go alone on his constitutional authority. To date, however, it has
always been resolved in the political arena without final constitutional determina-
tion by the courts, and without a head-on clash between the Congress and the
President. Whatever and wherever the line may be between congressional and
presidential authority a House committee accurately observes: “‘Acting together,
there can be no doubt that all the constitutional powers necessary to meet the
situation are present.’” H.R. Rep. No. 88-1708, at 4 (1964) (committee report on
Gulf of Tonkin resolution, quoting committee report on Formosa resolution).

II. Congress Has Affirmed the President’s Authority to Take
Necessary Action to Protect U.S. Troops in Southeast Asia

Although U.S. concern with the security of Southeast Asia dates from our
involvement there during World War II, it was formalized in the signing and
ratification of the Southeast Asia Collective Defense Treaty. The area covered by
the treaty includes not only the territory of the Asian signatories but also the States
designated in the protocol which was signed and ratified at the same time as the
treaty. These are Cambodia, Laos and the free territory under the jurisdiction of
the State of Vietnam. Pursuant to its treaty obligation, the United States for some
years maintained military advisers in Vietnam and provided other military
assistance to the Republic of Vietnam.
When U.S. naval forces in the Gulf of Tonkin were attacked in August 1964,
the President took direct air action against the North Vietnamese. He also request-
ed Congress “to join in affirming the national determination that all such attacks
will be met” and asked for “a resolution expressing the support of the Congress for
all necessary action to protect our Armed Forces and to assist nations covered by
the SEATO [Southeast Asia Treaty Organization]Treaty.” H.R. Doc. No. 88-333,
at 2 (1964).
On August 10, 1964, Congress responded with a resolution which “approves
and supports the determination of the President, as Commander in Chief, to take
all necessary measures to repel any armed attack against the forces of the United
States and to prevent further aggression.” Pub. L. No. 88-408, § 1, 78 Stat. 384,
384. It was in connection with this resolution that Congress noted that whatever
the limits of the President acting alone might be, whenever Congress and the
President act together “‘there can be no doubt’” of the constitutional authority.
H.R. Rep. No. 88-1708, at 4 (1964) (committee report on Gulf of Tonkin resolu-
tion, quoting committee report on Formosa resolution).
In the debates in the Senate on this resolution it is clear that the Commander in
Chief was supported in taking whatever steps were necessary in his judgment to
protect American forces. The floor leader, Senator Fulbright, noted on August 6,
1964 that the resolution “would authorize whatever the Commander in Chief feels
is necessary.” 110 Cong. Rec. 18,403. He observed: “In a broad sense, the joint
resolution states that we approve of the action taken with regard to the attack on

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our own ships, and that we also approve of our country’s effort to maintain the
independence of South Vietnam.” Id. at 18,407. When Senator Cooper inquired:
“In other words we are now giving the President advance authority to take what-
ever action he may deem necessary respecting South Vietnam and its defense, or
with respect to the defense of any other country included in the treaty?,” Senator
Fulbright replied: “I think that is correct.” Id. at 18,409.
The Gulf of Tonkin Resolution expresses broad support for the Commander in
Chief and recognizes the need for broad latitude to respond to situations which
may develop. Pub. L. No. 88-408, 78 Stat. 384 (1964). Of particular concern to the
Congress, as well as to the President, was the protection of American forces and
the security of South Vietnam.
While the Gulf of Tonkin Resolution was the first major congressional affirma-
tion of the President’s actions in responding to the situation in Southeast Asia, it is
not the only such affirmation. When bombing of military targets in North Vietnam
was undertaken in 1965, the President requested a supplemental appropriation for
the military. In his message of May 4, 1965, he emphasized:

This is not a routine appropriation. For each Member of Congress
who supports this request is also voting to persist in our effort to halt
Communist aggression in South Vietnam. Each is saying that the
Congress and the President stand united before the world in joint de-
termination that the independence of South Vietnam shall be pre-
served and Communist attack will not succeed.

H.R. Doc. No. 89-157, at 1 (1965).
The requested resolution was adopted on May 7, 1965. Pub. L. No. 89-18, 79
Stat. 109.
Since that time Congress has repeatedly adopted legislation recognizing the
situation in Southeast Asia, providing funds to carry on U.S. commitments and
providing special benefits for troops stationed there. There is long-standing
congressional recognition of the U.S. commitment in Southeast Asia.

III. The President’s Action With Respect to Cambodia Is Consistent
With His Obligations as Commander in Chief and With
Congressional Policy Regarding Southeast Asia

Recognizing that Communist troops have been occupying territory on the
Vietnam-Cambodian border and using it as a sanctuary from which to launch their
attacks into Vietnam and against American forces there, the Commander in Chief
has ordered limited incursions into this border area in order to destroy the
sanctuaries. He has made a tactical judgment consonant with his responsibility as
Commander in Chief, and consistent with the announced congressional policy of

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taking “all necessary measures to repel any armed attack against the forces of the
United States and to prevent further aggression.”
As noted in Part I above, from the time of the drafting of the Constitution it has
been clear that the Commander in Chief has the authority to take prompt action to
protect American lives in situations of armed conflict. Whether it be a formal war
declared by Congress or an undeclared war, it is the Commander in Chief who
determines how war will be made and what tactics are necessary to protect
American lives.
In ratifying the SEATO Treaty and accompanying protocol, Congress has
recognized the close security link among the various nations in the area. In
adopting the Gulf of Tonkin Resolution, it affirmed its determination to protect
U.S. forces in the area. In supporting the supplemental appropriation in 1965, it
recognized that the protection of U.S. troops and the prevention of infiltration
might necessitate going beyond the boundaries of South Vietnam.
The President’s action with respect to the Cambodian border area, limited in
time and in geography, is consistent with the purposes which the Executive and
the Congress have pursued since 1964. Whatever theoretical arguments might be
raised with respect to the authority of the Commander in Chief to act alone had
there been no congressional sanction for our involvement in Southeast Asia, there
is no doubt as to the constitutionality of the action in light of the prior affirmance
of Congress that the Commander in Chief take all necessary measures to protect
U.S. forces in Vietnam. Having determined the necessity, the Commander in Chief
has the constitutional authority to act.

WILLIAM H. REHNQUIST
Assistant Attorney General
Office of Legal Counsel

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