You're right. It would have been better for the troops in Vietnam, for LBJ, as bad as he was, to have had a second term. There would have been less anti-war demonstrations and LBJ would have shown some guts to the enemy by sticking it out, rather than tucking his tail under his leg and slithering back to Texas.
But that's, as you note, standard for the Democrats, as Kerry did the "Cut and Run Boogie" from "Nam", after only four months.
Notice how nobody in the present-day anti-war movement raised a single peep about Clinton's exploits in Yugoslavia, in a war that had absolutely zero national interest to the U.S., or posed any threat whatsoever to U.S. security.
The anti-war movement was conspicuous by its absence. It always is when the Democrats are in the White House. The anti-war movement is part of the Democratic Party.