Greatest election disaster in history

What would constitute the greatest election disaster in history?

1. People get infected from standing in lines to vote.
2. Mass fraud from voting by mail, (which we haven't experienced since its introduction in 1864),
3. The incumbent president loses.

The president should be thinking about #1, but talks #2, and probably just fears #3.
Trump doubles down on mail-in voting concerns, warns of 'greatest election disaster in history'