Here's Bob Dole on the current state of the Republican party: "I thought I was a conservative, but we’ve got some in Congress now who are so far right they’re about to fall out of the Capitol.”

So, is Dole, his party's presidential nominee in 1996, right?

To answer that, you first need to understand the idea of "asymmetric polarization" -- a fancy way of saying that while both parties have moved closer to their respective ideological poles in recent year, the Republican pole is far further to the right than the Democratic pole.

The idea of asymmetric polarization first came to my attention during the 2012 election thanks to this blog post on the VoteView website.  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.  The result is something called the DW-NOMINATE score.  (For a full explanation of DW-Nominate scores, click here but be warned: This is nerdy stuff.)

Asymmetric polarization burst into the broader consciousness when Tom Mann of the Brookings Institute and Norm Ornstein of the American Enterprise Institute released a book in the spring of 2012 called: "“It’s Even Worse Than It Looks: How the American Constitutional System Collided With the New Politics of Extremism". In an essay taken from the book, the duo wrote:

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

So, are we asymmetrically polarized -- with Republicans having moved further right than Democrats moved left?

Let's look at the VoteView analyses first. Remember that in their analysis, zero represents the ideological middle in Congress. The closer to 1.0, the more conservative. The closer to -1.0, the more liberal.  (It's worth noting that there is some dispute about the efficacy of the DW-NOMINATE scores. Sean Trende of Real Clear Politics has written smartly about his issues with using VoteView rankings to rate liberalism, conservatism and polarization. But, it's, to our mind, still the best/most comprehensive measure out there.)

Here's their chart for the House.

And here's their chart for the Senate.

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.

Now, we are big believers in supplementing the raw numbers with the eye test.  (Call it sabermetrics + scouting.) And, the eye test affirms the conclusions of the VoteView data.

Take John Boehner. Boehner, elected in 1990, was rarely called a "moderate" during his first decade in office. And, as we wrote last September, the totality of his record prior to his ascension as Speaker in 2011, was anything but moderate. (In 2010, Boehner received a 100 percent conservative score from the American Conservative Union and had a 94 percent lifetime score. That same year Boehner had a 100 percent rating from the conservative Club for Growth and a 83 percent lifetime rating.) Despite those facts, Boehner is widely regarded by a group of four dozen or so Republican House members as insufficiently committed to the conservative cause -- and is in serious danger of not being reelected as Speaker next year.

Boehner is just one example of a broader trend.  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.")

It's hard to argue based on the evidence above that we are not in an era of asymmetric polarization.  The Republican party that nominated Dole is not the Republican party that nominated Romney. It is simply more conservative. And, based on the last two years in Congress, there's every reason to believe it will be as -- or more -- conservative when the 2016 Republican nomination fight comes around.

Now, that is not to say that Republicans bare sole blame for the polarization in the country -- and the Congress. They don't. Here's VoteViews on that very topic:

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.

And, that focus seems unlikely to change -- particularly given the success of the '1 percent' argument in the 2012 presidential election, and the advice being given in high-level Democratic circles that the party's best strategy to avoid big losses this November is to re-adopt that basic message.

We are in historically polarized times. And there is little evidence that things will change any time soon.