There's an episode of the Simpsons where Mr. Burns brings in ringers for the company softball team. You might know it, because it's pretty much the best episode ever.
One of the ringers is Don Mattingly, a then-New York Yankee and current manager of the Los Angeles Dodgers. Mr. Burns has a problem with Mattingly's sideburns, which, as you may be able to tell in the picture to the left, are virtually nonexistent. Mattingly must shave his sideburns to play, and because he can't shave what doesn't exist (even though he tries), Mr. Burns benches him.
Michael Gerson would like Democrats to trim their goddamn sideburns.
Do politicians cause this polarization or merely reflect it? There are plenty of contributing factors they don’t control. The public itself has become more partisan over the past few decades. Both parties have become more ideologically homogeneous (though Democrats still have more internal diversity). The growth of partisan media has fed polarization.
But leaders can oppose this trend or contribute to it. Things get worse when Rep. Allen West (R-Fla.) claims there are “about 78 to 81 members of the Democratic Party that are members of the Communist Party.” Or when Rep. Debbie Wasserman Schultz(D-Fla.) says that Republicans “want to literally drag us all the way back to Jim Crow laws.” Politicians can legitimize incivility, contempt and conspiracy theories.
To be clear: Allen West accused about half of the House membership of being Communists, and, by extension, traitors to America. Debbie Wasserman Schultz compared laws that disproportionately affect the right of certain minority groups to vote to laws that disproportionately affected the right of certain minority groups to vote. (The difference, I suppose, is in the tense - the present tense is usually a sign of incipient anarchic revolution.)
What drives political polarization more than anything else is the continued assertion that all statements are created equally, and are therefore equally polarizing. If one side (say, a hypothetical political party called the GOB) routinely launches insane accusations (say, that a president is hiding his birth certificate or he's besties with Terrorist Jim over there), and the other makes hyperbolic but supportable statements in response, equating the former to the latter empowers the former. If anything you do is equally as bad as what the other guy does, the side less committed to any semblance of propriety or restraint is constantly justified in its actions by the very existence of the other side.
Imagine Guy A exposes himself to someone on the subway. Imagine Guy B wears an inadvisable swimsuit to the pool. Now, imagine we treated Guy A and Guy B exactly similarly, and tut-tutted both for their indecency and wished they could just stop. If you're Guy A, is there any reason to stop doing what you're doing if everyone's going to treat you like you're just a guy in a Speedo you never should have bought? Is there any reason not to escalate, because you're going to be continually treated as if you're a part of just more tiresome indecency?
Democrats and Republicans are not equally polarized or extreme or beyond the pale. They're simply not. And while Democrats are being yelled at to trim their sideburns, Republicans are walking around with muttonchops, because it's virtually the same thing.
(God, I love metaphors.)