While he is president, Trump can get away with things that anyone who is not president can't. He has explicitly said that
As has been stated by numerous legal scholars, I have the absolute right to PARDON myself, [...]
Because the Republican party – for reasons which I don't really understand – seem willing to support him to the edge of the cliff and beyond, he is essentially unassailable while he is president: he can do anything and get away with it.
But this ends once he is no longer president: the moment he is out of office the sky falls on him. And his crimes are very many and very serious: he will end up in gaol for a long time if he does not flee to (probably) Russia.
He knows this, and he knows what it means: he can never be out of office. He can not lose in November: if he can not win then the election must not be allowed to happen.
The most powerful man in the world is facing humiliation and flight, or humiliation and the rest of his life in gaol, and he will do anything in his power to avoid that. And the powers at his command are very great.
This is not a good situation.