There was never any plan for victory in Vietnam. There was nothing beyond the idea of putting on a show to prove our “resolve”.
You can see LBJ and Rob’t McNamara’s many memos to that effect in McMaster’s book on the war. Johnson was unwilling to allow a sufficient commitment to Vietnam to interfere with his Great Society domestic agenda.
Johnson was only willing to commit a fraction of what he was repeatedly told would be required to defeat the Communist conquest of South Vietnam. He had three lawyers designing his Vietnam strategy. The two Bundys and McNaughton IIRC. He had contempt for the senior military and ignored them.
Vietnam shows that when one side fights to win, and the other fights for a draw, the former will most likely be the outcome.