Because of gerrymandering and the political structure of the United States, Republicans have more to fear from a primary challenge on their right flank than they do from a general challenge on their left. It wasn't Democrats that took out John Boehner, it was Republicans. At some point we'll reach a point where not even the PACs will support this shit, but right now we've got a Republican Senate seriously debating the idea of denying healthcare to 33 million people just so they can get a "win" and make their moneymasters happy. We have an attorney general going balls deep into civil forfeiture. We have a climate change denialist in charge of the EPA and we have a key voting rights suppressionist on a special White House council. I think this doesn't stop this side of stacked bodies.
Your reference to the PAC's reminded me of the story I read today of long-time GOP donor Mike Fernandez. Apparently he left the Republican Party end 2016 due to Trump, and recently a Republican fund raiser made the mistake of asking for a contribution, at which point he replied: The cracks are starting to show.“All the Republicans who hide behind the flag and hide behind the church, they don’t have the f------ balls to do what it takes. [...] I am out of the political process. Too disgusted, too expensive, too supportive of ego maniacs whose words have the value of quicksand,” he wrote in an email to a Republican fundraiser seeking political contributions.
I sincerely hope you're right. So far they've lost George Will and Joe Scarborough and I guess Hannity isn't getting the Buckley Award because Chris Buckley said something along the lines of are you fucking kidding me my dad is spinning in his grave. But I'm not sure how much of the current posse is driven by opportunism vs. idealism. I think opportunism is heavily represented.