Betfair now giving Trump just a 49% chance of being the 2020 Republican presidential nominee, and Ladbrokes is giving him about the same. His chances of making it through his entire first term without leaving office early is bouncing around but in the mid-50s, so if he's not renominated, the market seems to think it'll probably be because he's out of office early (via either death, resignation, or impeachment), rather than because he stays in office but opts not to run again, or stays in office, runs again, but loses the nomination.
I actually think it is a very plausible scenario that he finishes his term but doesn't seek reelection and endorses Pence from day 1.
