He also attempted to sabotage the USPS, and cast doubts on mail-in ballots as a whole, with the obvious intent of suppressing opposition voters, and/or having reason to question the election after the fact.

The only party with anything to gain from suppressing voters are the Republicans. Look at the map of states that didn't ratify the 24th amendment. They've repeatedly made false claims of voter fraud, and engaged in voter intimidation and voter suppression.

And just this election, the Republicans put up fraudulent, illegal mail-in ballot drop boxes.