I was being facetious. Mostly.
As @some_guy pointed out, the Axis of Stupid (Drudge-Hannity-Carlson-Jones) used to get all het up over the prospect of martial law in the waning days of Obama’s presidency. I’d like to think I haven’t reached that level of paranoia yet.
On balance, I think @NovaeDeArx is right. Trump is willing to fight for stuff when he’s sure he’s going to win, but more often he simply declares victory and walks away. He probably won’t do anything as drastic as declaring martial rule, but if he did, who in the government would demur? Not the GOP, he’s broken the spirit of anyone who isn’t giving full throat to the Trump agenda. The Democrats aren’t positioned to do much until (please gods) November. And he’s the Commander in Chief of the military; I don’t think they can ignore his orders even if they want to.