Everyone knows, even those who deny they know, that Trump is guilty of multiple crimes, from bank fraud to campaign finance fraud, to suborning perjury, to tax fraud, to bribery (both giving and receiving), to violations of the emoluments clause of the constitution. Everyone also knows that the only reason he is not already under indictment is that he is currently President. As his remaining time in office drags on it seems certain that more and more crimes will be revealed. Mueller made a point of saying that since he couldn’t indict a sitting president, he was preserving the evidence for later.
We will eventually reach the point where a new President has been elected, but Trump is still around as a lame duck. At that point he will be starting to sweat about the indictments hanging out there waiting for him. Even Trump will see the obvious solution here: Do like Nixon. Resign early so that your vice-President can pardon you “for the good of the country, and so we can put this long national nightmare behind us.”
There is, of course, one small weakness in this scenario. It assumes rational and coherent thinking by a man who we already know is a delusional and pathological narcissist.