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.
Paris Peace Accords
However, as U.S. casualties had mounted throughout the conflict since 1965, American domestic support for the war had deteriorated, and by the fall of 1972 there was major pressure on the Nixon administration to withdraw from the war. Consequently, the U.S. brought great diplomatic pressure upon their South Vietnamese ally to sign the peace treaty even if the concessions Thiệu wanted could not be achieved. Nixon pledged to provide continued substantial aid to South Vietnam, and given his recent landslide victory in the presidential election, it seemed possible that he would be able to follow through on that pledge. To demonstrate his seriousness to Thiệu, Nixon ordered the heavy Operation Linebacker II bombings of North Vietnam in December 1972. Nixon also attempted to bolster South Vietnam's military forces by ordering that large quantities of U.S. military material and equipment be given to South Vietnam from May to December 1972 under Operations Enhance and Enhance Plus. These operations were also designed to keep North Vietnam at the negotiating table and to prevent them from abandoning negotiations and seeking total victory. When the North Vietnamese government agreed to resume "technical" discussions with the United States, Nixon ordered a halt to bombings north of the 20th parallel on December 30. With the U.S. committed to disengagement (and after threats from Nixon that South Vietnam would be abandoned if he did not agree), Thiệu had little choice but to accede.