August 7 - 1964 - The Gulf of Tonkin Resolution
The Gulf of Tonkin Resolution began large scale American involvement in the Vietnam War, which really had been going on for over a decade. America had even sent some troops, mostly military advisors, to support non-Communist South Vietnam against Communist North Vietnam, in the early 1960s. Then the USS Maddox reported an attack from North Vietnamese torpedo boats in the Gulf of Tonkin on August 2, with a separate attack reported on August 4. Although the evidence for such an attack was slim at the time and became even less credible later, President Lyndon Johnson wanted an escalation of American troops in Vietnam. Almost immediately, the United States Congress granted their approval. The Gulf of Tonkin Resolution was not a declaration of war, but an authorization for the increased use of force. This fact generally exposed a loophole in the Constitution whereby Congress declares War, but the President is the Commander in Chief of the Armed Forces. Eventually, the Resolution was repealed, and a War Powers Act would limit the scope of the President's general authority. The Gulf of Tonkin Resolution had already launched America into Vietnam by that point, however.