It was over a year... August 1974 to April, 1975, and when Nixon was in office, the South Vietmanese held their own. It was after the 1974 Congressional Elections and all aid to South Vietnam was stopped by a hard left Democrat Congress that South Vietnam fell, and the choppers lifted off, a holocause began, and the boat people suffered and died.
Click here for the "Watergate Babies" who cheered for that holocaust. Many of those bastards are still in congress.
I can criticize Nixon for a lot of things. But I can't blame him for the fall of Vietnam. He lived up to his promises as long as he was in office.
I also am not sure that Kennedy would have done more harm than Nixon did with his other policies.