I think for who the GOP nominates it's going to come down to what there stance was when the dam finally breaks and I don't mean impeachment necessarily. Just that moment when he quits, forced or otherwise. Were you with him or against him? Were you in his administration or not? Are you going to run on his alleged successes or apologize for his possible failures?
Nikki Haley was mentioned, I think she is the only one in his administration who could actually make a run for it, but she still has to carry his water to some extent. Mike Pence is far too conservative and represents the worst of establishment politicians and stood there with that dumbass look of consternation and bewilderment as he defended his master. He's only getting the golden ticket one way and that's if it ends very badly for his boss and then he will be an instant lame duck.
So, some n00b in Congress?