President-elect Donald Trump stunned the Pentagon and the broader defense world by nominating Fox News host Pete Hegseth to serve as his defense secretary, tapping someone largely inexperienced and untested on the global stage to take over the world’s largest and most powerful military.
I wouldn't hold out too much hope. They're also preparing to purge the military leadership:
https://www.rawstory.com/trump-generals/
I've been out a long time and was of low rank in any case. However, I'm skeptical that safeguards don't exist that will make that less effective than it sounds.
For one thing, the duty to disobey unlawful orders goes all the way to the lowest E1. (And when I was in, having grounds to refuse such an order and be justifiably defiant felt like Dobby hoping for Malfoy to give him clothes - it was unlikely, but I was always ready to go, and I don't think I was alone there.)
But I am doubtful that Trump can successfully reach a point where all or even enough of the top brass are willing to drink his flavor aid to not have to worry about them.
How often does this happen?
Dunno, but an awful lot has been written about it. We don't elect dictators very often, so I'd say we're in uncharted waters here.
https://duckduckgo.com/?t=ffab&q=soliders+who+have+disobeyed+unlawful+orders&ia=web