ASYMMETRICAL POLARIZATION…. The Washington Post‘s editorial board recently lamented polarization in American politics, and much to my chagrin, chalked up the problem to “the ideological purification of both parties.”

Brookings’ William Galston and Thomas Mann acknowledged the polarization, which is unrivaled in modern American history, but reminded the editors that “these developments have not produced two mirror-image political parties.”

We have, instead, asymmetrical polarization. Put simply: More than 70 percent of Republicans in the electorate identify themselves as conservative or very conservative, while only 40 percent of rank-and-file Democrats call themselves liberal or very liberal. It is far easier for congressional Republicans to forge and maintain a united front than it is for Democrats. George W. Bush pushed through his signature tax cuts and Iraq war authorization with substantial Democratic support, while unwavering Republican opposition nearly torpedoed Barack Obama’s health-reform legislation. When Democrats are in the majority, their greater ideological diversity combined with the unified opposition of Republicans induces the party to negotiate within its ranks, producing policies that not long ago would have attracted the support of a dozen Senate Republicans.

Consider the episode that The Post cited as Exhibit A for polarization: Sen. Robert Bennett’s commendable work with Democratic Sen. Ron Wyden to develop a bipartisan health bill, which was used against him by conservative Utah activists to deny him renomination. The Post failed to note, however, that Senate Republican leader Mitch McConnell pulled the plug on the Wyden-Bennett initiative well before health reform was taken up last year.

Bennett and other Republican co-sponsors of this bipartisan bill were told in no uncertain terms that the party strategy was to block every major domestic policy initiative of the new administration and not to engage in substantive negotiations that could produce bipartisan majorities on the floor. During the lengthy health debate, not one Senate Republican spoke in support of the Wyden-Bennett bill. Tea Party activists outraged at Republican incumbents for cavorting with the enemy (i.e., Obama and the Democrats) took their cue from Republican Party leaders.

The media establishment is no doubt uncomfortable with this reality — though I give kudos to the Post for running the Galston/Mann piece — but here’s hoping the “both sides are always equally wrong, even when they’re not” crowd takes note.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.