The Gulf of Tonkin Resolution was an act of Congress in 1964 that effectively gave the president carte blanche in using force for the Vietnam War. But Congress never actually declared war against Vietnam. So was this constitutional? How did this shape the president’s authority to use military force going forward? Let’s start from the beginning.
The Constitution declares the president the Commander-in-Chief of the armed forces but gives Congress the power to declare war. This presents the potential for a conflict but amazingly, very few problems arose until the turn of the 20th century. See, for the first century of American history, the nation’s leaders abided by a foreign policy of isolationism. It started with George Washington’s farewell address in which he warned the fragile nation to stay out of foreign entanglements and alliances. Later, foreign policy was dictated by the Monroe Doctrine of 1823, presented by President James Monroe and largely designed by his Secretary of State John Quincy Adams. The doctrine states that the New World and Old World were separate spheres of influence. Europe will say out of our backyard and we would stay out of theirs. It is largely why America was late to the colonization game and had very few colonies in Africa and Asia.
But as the United States became an industrial powerhouse and emerged on the world stage, foreign entanglement became inevitable. The Spanish American War in 1898 was the first reach outside of the United States but was still within the Monroe Doctrine as the United States was fighting against Spain within its Western Hemisphere colonies. The doctrine was later reinforced by President Theodore Roosevelt in 1904. His corollary stated that we should not only protect the Western Hemisphere from European colonization but that the United States should preemptively intervene in Western Hemisphere countries so others do not. His famous advice was to “speak softly and carry a big stick.”
World War I brought a debate as to whether or not America should get involved. The debate raged on as US involvement became more inevitable in World War II. Some isolationists still existed though. The Ludlow Amendment, proposed several times between 1935 and 1940 by Congressman Louis Ludlow (D-Ind.), stated that a national referendum should be required to declare war, except if the United States was attacked first. He argued that if ordinary people are to fight in the wars, they should be the ones to approve of them. The amendment, of course, was never passed.
World War II was the last time Congress declared war. In fact, for all of the United States military involvements, Congress has only declared war 11 times over five wars (Great Britain in the War of 1812; Mexico in the Mexican-American War; Spain in the Spanish American War; Germany and Austria-Hungary in World War I; and Japan, Germany, Italy, Bulgaria, Hungary, and Romania in World War II). The Korean War was the first major conflict in which the US did not actually declare war. In fact, it was the first war that did not have Congressional approval but instead only approval from the United Nations Security Council. There had be instances in the past where military force was used without a declaration of war but they all had accompanying Congressional acts.
Then came Vietnam. At first, Congress overwhelmingly approved unlimited use of force after an American ship was attacked (though this is up for debate) in Vietnam’s Gulf of Tonkin in 1964. The United States had initially sent troops years earlier, but this was an approval for any force needed. By the 1970s, the war was dragging on and had no end in sight. Congress became concerned that the war was only intensifying but without a declaration of war. They also feared that their influence over military entanglements was greatly diminished by the 1964 act. So in 1973, Congress passed the War Powers Resolution. The law says that the president must notify Congress within 48 hours of committing forces to military action. It further states that the military can only stay 60 days, with an added 30-day withdrawal period, unless Congress approves further action. President Nixon vetoed the bill but Congress overrode his veto making it the law of the land.