The Americanization of the Vietnam War thus arrived at a time when Congress as an institution was looking for new avenues to shape U.S. foreign policy. Until 1964, Congress had played a fairly minor role on Southeast Asian matters. In 1954, Eisenhower had invited legislative leaders to comment on whether the United States should use its military to rescue beleaguered French forces at Dien Bien Phu. But the president had little desire to send troops and almost certainly engaged in the charade so he would have an excuse to explain his lack of action to the French. The Kennedy years featured a more consistent level of congressional comment. Many of the same critics of foreign aid—Gruening, Gore, Church—also questioned the military and economic assistance program toward the dictatorial government of Ngo Dinh Diem and called for Congress to more aggressively counter administration policy. But at no point did a sustained legislative effort on Vietnam policy emerge.
That condition changed after Lyndon Johnson assumed the presidency in November 1963 and military conditions in Vietnam began to deteriorate. With only one exception, Johnson accomplished his goal of keeping public attention off Vietnam until after the 1964 elections. But that exception resulted in one of the most famous pieces of legislation in the postwar Congress. In August 1964, after North Vietnamese vessels reportedly attacked U.S. forces in the Tonkin Gulf, the administration introduced a resolution granting the president authority to take all necessary measures to repel the attack. The open-ended wording disturbed some senators, but the chair of the Senate Foreign Relations Committee, J. William Fulbright, assured his colleagues that Johnson would never utilize the full breadth of the authority the Tonkin Gulf Resolution granted him. Although in retrospect Fulbright's words ring hollow, at the time his assertions seemed perfectly reasonable. Eisenhower and Kennedy had introduced similar offerings to deal with specific crises, and these had not resulted in a massive commitment of U.S. troops overseas.
By mid-1965, however, the increasing numbers of U.S. troops in Vietnam prompted a more active congressional response. For the rest of Johnson's term and most of Richard Nixon's, an increasingly powerful group of Senate liberals tried to end the war through congressional action. Perhaps their most important initiative came in 1966, when Fulbright convened public hearings on Vietnam policy that attracted a national television audience to witness divisions among the foreign policy elite regarding the administration's approach to matters in Southeast Asia. Indeed, although members of Congress failed to prevent the Americanization of the Vietnam conflict, their activities did help turn U.S. opinion against the war. In the process, Fulbright became the most powerful Foreign Relations Committee chair—and, perhaps, the most important congressional player on foreign policy matters—since William Borah in the 1920s.
Beyond the antiwar activities of Senate liberals were two other substantial areas of congressional involvement in 1960s foreign policy. The first centered on the wartime actions of congressional Republicans and prowar Democrats, such as Senators John Stennis (Democrat) and John Tower (Republican) and Representative Gerald Ford (Republican). Stennis and Tower were particularly significant because their extensive contacts made them the Capitol Hill voices for the military at a time when the Pentagon was often articulating its own perspective on international affairs. Second, quite apart from Vietnam, Senate liberals challenged Cold War principles elsewhere in the world. Because their dissent did not fully blossom until the United States already had tens of thousands of troops on the ground in Vietnam, Senate liberals always acted under some constraint. The full force of their perspective emerged only in their positions on newer issues—such as Greece, where they demanded a cutoff of U.S. aid after the military coup of 1967, and Thailand, where their anti-interventionism offered a clear sense of their desired role for the United States in Southeast Asia.