It’s going to be ugly. David Cay Johnston (boldface mine):

There is no good ending to the story. America will survive this, we’ll get past it, but whenever Trump leaves, there’s no good ending. If Trump is removed by impeachment or by the voters, whether in a Republican primary or a general election, I know what he will do. He’s already told us what he will do by his actions. Trump will spend the rest of his days fomenting violence and revolution in this country.

He’s careful not to directly say “revolution,” but he will call the government illegitimate. He might even call it criminal, since he called Democrats who didn’t stand up during his State of the Union speech treasonous. If they’re going to impeach Trump, I believe they have to have a plan to indict, try, convict and imprison him. But Trump will be a role model for some people, and there may well be violence over it.

No matter what, Il Trumpe will be the first ex-presidential troll. If he does not serve out two full terms, it will be especially ugly. Since his base thinks he can do no wrong, there will be a core group of millions who think if Trump doesn’t serve two full terms, something illegal happened.