For many GOP lawmakers, even that wouldn’t be enough. Many have indeed shown that they’ll back Trump no matter what. But it is not that hard to imagine a set of facts that would cause principled Russia hawks like Ben Sasse, Marco Rubio, and Lindsey Graham to turn against the president. And once a few dominos fall, it makes it easier for the others to topple in turn.
Remember, too, that the two biggest reasons that Republican lawmakers continue to back Trump is that they see him as a vehicle to accomplish their legislative goals, and they fear a backlash from the Trump-loving base were they to turn on him. But in a post-midterm world in which Republicans have been roundly shellacked, Trump’s legislative agenda would be dead on arrival, and his base would be disillusioned. Republican senators might well see fewer reasons to stand by their man.
Of course, a lot would have to happen to get us to this point.