Cut stuff in Kentucky. See how fast his tune changes.
Well, I wouldn't hurt the people of KY. What I would do instead is have lots of rallys in the state, letting the citizens know what a lousy job their Senator is doing for them, and encouraging them to storm the local offices demanding change. Light a fire under Mitch's butt, make his life (and the life of his aides) miserable, and maybe he'll come around to the right way of thinking.
If he's a good boy and helps Trump, then help his re-election in 2020. Otherwise, campaign against him.
In short, give 'em hell.