The court system is loosely based on public opinion. Since it’s unreasonable to gather the public’s opinion, a jury is selected to represent “the public”.
In this case, the election essentially allows you to get the actually public’s opinion. You literally cant get closer to true “court of public opinion” that having a nationwide vote on a recently convicted individual candidacy.
He can’t do that. These are state crimes.
He has no authority to pardon non-federal crimes.