It’s like he’s saying, “Fire me, I won’t serve under a President Trump.” In that case he should resign.
But, he may figure if a number of (well warranted) Trump military firings can be made political, he’ll be lauded as a martyr for “the cause.” He’s probably has a good retirement secured anyway. This will raise his post-military visibility considerably.
Maybe he could parlay that into a gig hawking reverse mortgages.
Well, maybe he is confident of a good gig at CNN being their “expert Navy authority” and spend his time trashing Trump....that ignorant country bumpkin. /s