I don't really think "forgiveness" has anything to do with it.

This is who Trump is - someone who will try to destroy anyone, no matter how virtuous or good for the country - who isn't an obsequious toady.  If he wins, he'll keep doing it after the election to any Republican who doesn't 100% support him no matter what he says or does.  Almost inevitably, he'd leave the party in much worse shape than if/when he takes office.

Expressing regrets - which he would never do and would never mean anyway - is worthless.  He's just a guy to whom principles mean nothing, and everything is just about him and his ego.  I despise him as much as I despise Biden.