Which of these was the worst mistake made by a U.S. President?

[Pericles]

Nobody died in Watergate. LBJ's decision to enter the US into a disastrous war undermined trust in government too, it was a political mistake as it destroyed his presidency and split the Democratic Party, without it LBJ would have run and won in 1968 and the Democrats would likely have governed until 1972 or 1976. It also resulted in the deaths of thousands and undermined America abroad. I'll say Vietnam.