Veteran here, who also lives near a Marine base and whose friends are almost all active duty Marines:
Enlisted ranks will obey their commanding officers. Their commanding officers are all college educated, and a lot more liberal than they are. That is not to say that there’s aren’t Trump lovers in the officer corps, but you will find few members of the personality cult. You will find lots of high ranking officers like Jim Mattis and Mike Esper, whose allegiance is to the office is unshakable.
Now there may be some question come late 2020 who that office holder IS. I fully expect Trump to fight, he may win, he may lose. Whoever is legally president on Jan 20th, 2021, even if it’s by a coin toss, the military will follow and make sure is installed into office, no matter what any of the ranks’ personal thoughts are.