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

[Blue3]

I don't know how it's so close between Vietnam and Watergate.

One was about an ethical concern, that led to a president's resignation. To be replaced by Ford and then Carter. No lives ruined. No big change for the Republicans or Democrats, for the liberal movement or the conservative moment. It just was another reason for people to become more skeptical of government, and some skepticism is a good thing.

The other was a miscalculated war with no end in sight, leading to the deaths and mutilations of tens of thousands of Americans (including draftees, not just volunteers) and much more for the people of SouthEast Asia, to support a government that wasn't even that great, that led to the ruin of a President and forcing him to quit re-election, and ruined his party for years in ways the Democrats still haven't completely recovered, tainting his legacy in other areas too, leading to distrust in government, etc. etc. etc.

There's no comparison.