Trump will run for re-election because the second he is out of office he’s vulnerable to prosecution and won’t have the GOP’s DOJ to protect him.
Ah, Bibi's playbook.
I wasn't really around then, but it's happened before:
https://www.history.com/news/lbj-exit-1968-presidential-raceLBJ leaving the '68 race looked like a 0% chance right up until he made his withdrawal announcement at the end of the State of the Union.
As for Trump, it mostly concerns:
1) how the virus plays out, how many die, how long it persists, and how bad the post-mortem is on Trump's inept leadership. The lack of a coordinated national policy has been devastating.
2) there are plenty in the Repub party who don't like Trump and would love to see him removed, even disgraced, and a more normal standard bearer in his place.
Look at how the Dems just thwarted Bernie -- though this would obviously be on bigger scale.
3) poll numbers, how discredited Trump becomes, his state of mind. Trump could just say the hell with it, and prefer to go back to his business empire. While many could be hugely tired of him. Trump's failed and moved on before.
4) these have been strange times, with 2 impeachments, the Supreme Court deciding another election, rich buffoon Trump getting elected, I wouldn't be shocked by one more shock.