On August 4, 1964, President Lyndon Johnson announced that two days earlier, U.S. ships in the Gulf of Tonkin had been attacked by the North Vietnamese. Johnson dispatched U.S. planes against the attackers and asked Congress to pass a resolution to support his actions. The joint resolution “to promote the maintenance of international peace and security in southeast Asia” passed on August 7, with only two Senators (Wayne Morse and Ernest Gruening) dissenting, and became the subject of great political controversy in the course of the undeclared war that followed.

The Tonkin Gulf Resolution stated that “Congress approves and supports the determination of the President, as Commander in Chief, to take all necessary measures to repeal any armed attack against the forces of the United States and to prevent any further aggression.” As a result, President Johnson, and later President Nixon, relied on the resolution as the legal basis for their military policies in Vietnam.

As public resistance to the war heightened, the resolution was repealed by Congress in January 1971.