See my previous comment. There are a ton of restrictions placed on a sitting president.
After four years of being told what you can't do by the secret service, how sure are we that Trump will still want the job.
Trump likes to win, so that might inventivize him to try again, but I'm not sure he is going to love the work of actually being president. Dissatisfied Republican establishment might even give him a primary challenge (I assume party rules allow that).