Well, the blood is in the water. Republicans are sick of this, McCain has called this a Watergate situation and people are no longer defending him that much outside of the right wing media. Even Fox exposed its poor viewers last night to the bad news.
The thought of Mike Pence being in charge has to make GOP feel good but taking down Trump could get pretty ugly and the Democrats could make the Republicans do the heavy lifting.
There is this, the 25th Amendment:
Section 4.Whenever