Of the many frustrating things about political punditry, one of the most frustrating is the extent to which many writers choose to ignore core facts about our political world and instead rely on generalities, intuition, and lazy conventional wisdom. For one great (terrible?) example of this, look no further than the most recent column from Gerald Seib of the Wall Street Journal, in which he blames the near-collapse of the fiscal-cliff deal on "both sides":
There are multiple reasons that even what seems easy is hard in Washington right now. The problems start, of course, with the basic polarization of not just Congress but the country. America is in an unusual political state, in which the two parties are quite evenly divided in power, but far apart ideologically. […]
In the House, there is almost no middle ground, and the vote there Monday night was far more divided along partisan lines. Most members come from such reliably Democratic or Republican districts that they simply feel no pressure back home to compromise with the other side. Indeed, in this fall's election, 125 House members won their districts with 70% or more of the vote. Such margins leave House members thinking they have their own personal mandates to stick to their guns.
Even a casual observer of negotiations over the fiscal cliff knows this isn't true. Even if you ignore the whole reason for the fiscal cliff-Republicans threatened to default on the debt if the White House didn't agree to spending cuts-we just witnessed two weeks of GOP intransigence, as right-wing lawmakers rejected everything from a balanced deal crafted by President Obama and House Speaker John Boehner, to a intensely conservative deal introduced by Boehner himself. And indeed, the final agreement passed in spite of GOP opposition-only 85 House Republicans out of a conference of 242 voted for the deal. The remaining 172 votes came from Nancy Pelosi and House Democrats for a final count of 257 to 167.
To be fair, these are just anecdotes. You could argue that this was just an exception to Democratic intransigence. But you'd be wrong. Over at the Voteview blog, political scientists Christopher Hare, Nolan McCarty, Keith Poole, and Howard Rosenthal put data behind the contention that the GOP is responsible for the intense polarization of Congress:
[W]e find that contemporary polarization is not only real - the ideological distance between the parties has grown dramatically since the 1970s - but also that it is asymmetric - congressional Republicans have moved farther away from the center than Democrats during this period. In two figures below, we plot the mean first dimension DW-NOMINATE scores of the two parties in the House and Senate from 1879 to the present. Since the mid–1970s, Republicans have moved further to the right than Democrats have moved to the left.
And the Democratic shift to the left has less to do with the development of more liberal positions, and everything to do with the disappearance of conservative Southern Democrats. When you account for that, "the northern Democrats of the 1970s are ideologically indistinguishable from their present-day counterparts."
It's open question as to whether polarization is a problem-not only is it the inevitable result of democratic politics in an open and diverse society, but it helps build enthusiasm for participating in the political process. We'd be better off ignoring polarization, and focusing on ways to accomodate it in our institutions.
But if you do see polarization as an obstacle to overcome, then you should direct your attention to the Republican Party. To say that it's a problem of both sides is to live in a fantasy world.