History of the United States (1964–1980)
The growing Watergate scandal was a major disaster for Nixon, eroding his political support in public opinion and in Washington. However he did manage to secure large-scale funding for South Vietnam, much of which was wasted. The United States withdrew its troops from Vietnam before the Paris Peace Accords in 1973. However, Watergate resulted in significant Democrat gains in the 1974 midterm elections and when the new 94th Congress convened the following January, it immediately voted to terminate all aid to South Vietnam in addition to passing a bill forbidding all further US military intervention in Southeast Asia. President Ford was against this, but as Congress had a veto-proof majority, he was forced to accept. South Vietnam rapidly collapsed as the North invaded it in force, and Saigon fell to the NVA on April 30, 1975. Later nearly one million Vietnamese managed to flee to the U.S. as refugees. The impact on the U.S. was muted, with few political recriminations, but it did leave a "Vietnam Syndrome" that cautioned against further military interventions anywhere else. Nixon (and his next two successors Ford and Carter) had dropped the containment policy and were not willing to intervene anywhere.
USS Blue Ridge (LCC-19)
The final descent of the Republic of South Vietnam: 
"On the evening of 20 April, ... conducted a successful withdrawal from Xuan Loe, ... Overshadowing the military consequences of this withdrawal were the political consequences. ... The following day, President Thieu resigned ... Vice President Tran Van Huong. the president's constitutional successor, replaced Thieu. His term lasted a week. ... the National Assembly designated General Duong Van "Big" Minh to replace Tran Van Huong as President of the Republic of Vietnam.' ... On the evening of 28 April, with Saigon nearly surrounded, General Minh took the oath of office. ... within minutes of the ceremony, a flight of captured South Vietnamese A-37s bombed Tan Son Nhut. ... convinced the new leaders of the republic that they had but two choices: negotiate or capitulate. ... Ambassador Martin returned to the Embassy and made his decision ... and called Secretary of State Kissinger, he officially relinquished control of the evacuation of South Vietnam. In less than 20 minutes, it became a military operation. At 1051 29 April 1975, USSAG passed the word to execute Frequent Wind's Option IV. ... General Minh. ... told his soldiers to lay down their arms. On 30 ApriI 1975. the Republic of Vietnam ceased to exist. "