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.