How? Threaten him with what? Removal as majority leader? All McConnell needs are the votes of 26 Republican Senators to remain leader. That is a piece of cake for him, given the way the Senate GOP feel about the President. Issuing a completely empty threat would accomplish absolutely nothing and would just make the President seem even weaker.
Good point. But there must be some things Trump could threaten him with. Holding rallys in Kentucky to get people riled up? Encouraging them to melt Mitch's phones?
I dunno. I'm sure some here can think of actual, effective things.