The United States Did Not Lose the war in Vietnam
The US DID NOT "lose" the war in Vietnam. The Nixon administration chose to not win it.
Nixon, in effect, continued the ugly, bloody, wretched core of the Lyndon Johnson/Robert McNamara policy. This was the Johnson policy to not win [aka thinking to win on the cheap, with "just enough" force; thus endless, too-small escalations, and micro-managing from the White House; one must ask, too, how bloody are the hands of the Joint Chiefs of that day?].
Johnson and McNamara proved beyond doubt their incapacity to understand the core truth of war.
The LSM had tired of the war, reported their version of it [just as they do today from Iraq], and, convinced it knew best, made sure the country turned against it.
The "Nixon gambit" off the Johnson plan was to bring enough destruction not to win, but to strike a deal to get out not-quite-precipitously.
So Nixon's "choice" [he may have had other "options," but only in theory] was to broker an armistice. That's not a loss, it's an agreement to walk away.
And that was tragic, because with that done, it was South Vietnam that immediately lost its war to survive. It had no place to walk away to. And millions of people throughout Indochina lost their battle to survive against Communism, the bloodiest ideology of man to date.
"War is cruelty. There's no use trying to reform it. The crueler it is the sooner it will be over."
-William Tecumseh Sherman
Note the absence of qualifiers in the following statement:
"You ask, what is our aim? I can answer in one word. It is victory. Victory at all costs. Victory in spite of all terrors. Victory, however long and hard the road may be, for without victory there is no survival."
~~ Prime Minister Winston Churchill
Addendum: Let me make clear that the media bear their large share of guilt in this. I'll use Jesus's observation on lawyers to make illustrate the point: "for ye lade men with burdens grievous to be borne, and ye yourselves touch not the burdens with one of your fingers."
~~ Luke 11:46