Republicans are immune to their own extremism...for now. by @DavidOAtkins
But for most Republican legislators staring down the next few election cycles, the biggest threats still come from the right rather than the left or the middle. Extremism, in short, will be rewarded.
Most centrist pundits don't want this to be true. There is a cottage industry in pundit land to declare that Americans are basically centrists or center right, and that extremism on either side will be punished. Political parties are seen as polarizing influences and necessary evils at best, clouding the natural agreements that most Americans share about public policy.
But the reality of American politics is very different. There is a liberal America mostly concentrated on the coasts, highly educated populations, heavily minority populations, and in larger urban areas. There is a conservative America concentrated in whiter, more exurban and rural areas. There's frankly not that much in between. One of the reasons that the Affordable Care Act has such tepid support is that most Americans are either against it completely, or would prefer something stronger. Most Americans want to increase taxes on the wealthy; the minority who oppose that policy want to cut them. Most Americans favor significantly stricter gun controls; those who don't are adamant about relaxing them. There's very little constituent support on most policy issues for a centrist, Third Way approach.
America, then, is a polarized nation. But it's not equally polarized. It's clear to almost everyone that the Right has shifted dramatically farther to the right, while the left has only shifted leftward on a smattering of social issues such as gay rights, but mostly shifted rightward on issues like economics and civil liberties. The politics of Eisenhower and Nixon on economics and foreign policy would find themselves comfortably at home on the leftward side of the Democratic Party, while Ronald Reagan would be considered a RINO in today's Republican Party.