"As far as the "domestic" forces, and I am assuming you mean the troops not actively involved in RVN, we spent a lot of time training to fight the Soviet threat. The Korean peninsula heated up at the same time; it appeared the North Koreans were testing our resolve there."
Good point. What many forget is that, less than 15 years before, the US had just emerged victorious from a bloody Pacific war in which tens-of-thousands of Americans (and British, Canadians and Australians)were killed or wounded. Does everyone think they detroyed Japanese imperialism in the Pacific just to walk away and let the commies take over? In spite of it all, the US will be shown to have been right in its VN involvement. Even though the war was lost by the US (or, really, it was one theatre in a global conflict. In this respect, it lost the battle, but won the war.), it demonstrated America's resolve, its attempts to keep its word to its allies, and kept enough Russian and Chinese resources busy to blunt the threat until the communist system was shown to be what it was: an unworkable Utopian idea, which lent itself all-too-easily(as most Utopian ideals) to dictatorship and btutal tyranny.
Ouch! I always have a problem with that perception....true, the communist north defeated the forces of RVN, but not until a couple of years after the last combat troops left Viet Nam.
When JFK first ramped up the advisors to RVN, the purpose was to assist RVN in it's effort to fight off a communist take over. When it appeared, more was needed, LBJ ordered the escalation of American involvement. (both Democrats....hmmmm.)
I am purposely leaving out the political considerations that led to these decisions; too many to discuss in this post.
In 1968 after TET the communists were so weak, the war was winding down, but a bizarre chain of events involving many puppets on this stage we call life came into play or became more prominent.
The decision to stop the bombing in the north.
The decision to allow the build up of material and men just across "neutral borders", the efforts of SOG notwithstanding.
McNamara's often strange advice on the way to conduct the war.
LBJ's decision to not run again.
The election of RM Nixon and the perception/belief of the American public that he must/should withdraw the troops.
Kissinger's selection.
The idiotic misinformed statements of Uncle Wally about the unwinnable war.
On and on.
A lot more came into play in the decision to leave RVN and let them carry the fight, but I believe, America did not lose that war, the Vietnamese did, and the only egg on our face was our lack of re-intervention in 1975. It created a world wide suspicion of American resolve, for which we are still paying the piper.