Oh come on. Donald Trump scares the crap out of Mitch McConnell and every other incumbent politician. They already know they can handle Rubio. They already know they can neutralize Ted Cruz. They have been there and done them both.
I doubt they’re all that worried. Trump signaled a while ago that he’s on their side. Between endorsing McConnell, attacking Cruz for not getting along with McConnell, and his belief in the importance of making more deals with the establishment of both parties , Trump seems pretty willing to be on their side.