My understanding of events, gleaned several years after the fact, is as follows. We bombed North Vietnam back to the peace table. We negotiated a deal. We had an orderly removal of troops, but for a few at the US embassy. It was understood that we would provide financial aid to our ally, South Vietnam. In case of a conventional invasion by the North, we would provide military assistance.
After Watergate, the new Congress was very Democrat and very liberal. They cut off aid to South Vietnam and passed a law prohibiting military assistance to South Vietnam under any circumstances. This was an open invitation for the communists to resume the war. Two years later, South Vietnam fell.
The US won the war, then abandoned an ally. Liberals did not care. They thought communism would be better for South Vietnam and the region. History has proved them wrong.
I think part of it was also war weariness, and I sort of think we had attained our strategic objective. in ‘64, it seemed Communism was monolithic, that the combined USSR/Red China were likely to be a very powerful enemy. ( That would have been a commoner’s point of view; I guess they were already much at odds in reality) . National Review formulated a theory that was very much a part of my thinking in those years, namely that moscow’s agent in Peking, I believe in was Lin piao, but I may be wrong , was vying with Chou en Lai for dominance, but that he was killed in a plane crash in 1969, I think in Mongolia, “while fleeing to Moscow.” In any case, Nixon going to Peking, meeting with Chou en Lai, etc., more or less openly proved there was no monolithic Communism anymore, that’s by 1972. So I think strategically, it was a holding action while the dynamics between USSR and Red China clarified. In that sense, always saw it as a victory. But that’s only from a teenager’s evaluation of what was happening.