The Morning Joseph types have a new thrill running up their legs because Mittens said some slightly not nice things about Trump in their local gossip sheet.
As with Sasse and Flake and occasionally Corker and all the Never Trumpers, the distance between Trump and him on policy is wafer thin, in part because aside from "give rich people all the money and keep the defense industry happy," he and they don't know or care much about policy. Romney's just positioning himself to be the 2020 savior, as the scrolls foretold.
The thing is, you can, as a senator, constructively oppose the worst of Trump without turning into a Democrat. Romney isn't a Democrat and he isn't even a centrist, even if the senator from Utah played one for awhile when he was governor of his home state of Massachusetts. But he doesn't have to start agreeing with Sherrod Brown on everything to oppose Trump. One senator can be a giant pain in the ass in the world's greatest deliberative body if they want to. This is true, also, too, of Democrats in the Senate, but Romney could do so and get endless praise heaped on him by Morning Joseph instead of being labeled an obstructionist.
But he'll just join the Sunday show furrowed brow club, concerned about Trump but strangely powerless to do anything about him.