They kind of have to, that's explicitly in the rules for the military. You're more than welcome to
have a political opinion in the military but you are absolutely not fucking allowed to make a public showing of it. Where political affiliation is concerned, via the UCMJ, First Amendment protections are not extended to the military to the same extent that it extends to civilians; in the military, you're actually limited pretty substantially when it comes to political expression.
To the absolute best of my knowledge, you are
not allowed to overtly say that you're "never Trump" because that directly implies that you're openly against the President of the United States, and as a high-ranking military official that's
really not-- Oh, nevermind, he
officially retired sometime back in July and I missed that in the shuffle.
Alright, fuck it. Fair enough.