In Chris Cillizza’s “Bob Dole says the GOP is way more conservative than it was even 20 years ago. He’s right.” at The Fix, he analyses a VoteView study of roll call votes in the U.S. House and Senate to show that the Republican Party has indeed become more ideologically-extreme.

…What VoteView did is analyze every roll call vote in the House and Senate and then use that data to map how liberal or conservative the average Republican and Democrat was over time…If you start in the early 1990s, you begin to see the Republican and Democratic lines heading in opposite directions — with Republicans growing more conservative and Democrats more liberal. (This is true in both houses of Congress although more stark in the House.) But, the charts also show that Republicans have moved closer to the 1.0 pure conservative score than Democrats have to the -1.0 pure liberal score. That movement has been even more pronounced in the last decade in the House.

He quotes from the landmark Brookings study by Norm Orntstein and Thomas Mann, “It’s Even Worse Than It Looks: How the American Constitutional System Collided With the New Politics of Extremism“:

We have been studying Washington politics and Congress for more than 40 years, and never have we seen them this dysfunctional. In our past writings, we have criticized both parties when we believed it was warranted. Today, however, we have no choice but to acknowledge that the core of the problem lies with the Republican Party…The GOP has become an insurgent outlier in American politics. It is ideologically extreme; scornful of compromise;unmoved by conventional understanding of facts, evidence and science; and dismissive of the legitimacy of its political opposition…When one party moves this far from the mainstream, it makes it nearly impossible for the political system to deal

Speaker Boehner, who bosts top ratings from conservative organization groups is often dissed by his GOP colleagues as inadequately conservative. Further, adds Cillizza:

Republican politicians who were once considered solid conservatives two decades ago are now routinely dismissed as Republicans In Name Only (RINOS). The defeat of Bob Bennett in Utah in 2010 and the primary challenges to the likes of Sens. John Cornyn (Texas) and Mitch McConnell (Ky.) are evidence of this trend. Conservatism tinged with pragmatism is no longer considered conservatism by many within the party’s base. Sen. Ted Cruz, the most visible figure of the ‘pure’ conservative movement, typified the change within the Republican party in Congress when he recently dismissed Dole, John McCain and Mitt Romney as evidence that when Republicans don’t stand on principle, they lose. (Dole’s response? “I was one of the top supporters of President Reagan and had a pretty conservative record when I was in the Senate. But he [Cruz] didn’t know any of that.”)

Cillizza quotes from the VotewView study:

Though Democrats have not moved nearly as much to the left as the Republicans have to the right, they have also contributed to polarization, in our opinion, by embracing identity politics as a strategic tool. In Roosevelt’s New Deal, the Democrats advocated redistribution and regulation of business. These issues remain active to some extent, but with time emphasis has shifted to issues centered on race, gender, ethnicity, or sexual preference. As this issue evolved, it mapped onto the existing liberal-conservative dimension. The mapping is marked by members of the Black Caucus anchoring the liberal end of the dimension. What our roll call analysis shows is that Democrats did not vote much further to the left on the new issues than on New Deal issues. The comparison works because some New Deal issues, such as minimum wages and regulation of the financial sector, continue to lead to roll call votes.

Well, it’s not so easy to avoid “identity politics” when your group is targeted for discrimination based on “identity.” Cillizza concludes with a shrug, acknowledging that the attack on 1-percenters’ worked pretty well in 2012, and we should expect more of that going forward.
Another way of saying it is that Democrats have reconnected with grass-roots populism, and it seems to be working well, while the Republicans have drifted even farther toward the hard, unbending right.