Last week, I participated in a conference called "American Gridlock: Causes, Characteristics, and Consequences of Polarization," hosted by Jim Thurber and Antoine Yoshinaka at American University. While many conferences on American politics feature mentions of polarization, this one focused on it exclusively, and it was fascinating to hear so much great research examining polarization from so many different perspectives.
One key lesson from this was that polarization is not just a figment of the imaginations of Washington reporters. This stuff is real. We saw evidence that voters seem to be polarizing, although there was interesting debate over just what that means. (Are they just sorting themselves out into like-minded communities? Are regular voters actually thinking more ideologically?)
We also saw further evidence of Congressional polarization, with Congress increasingly hamstringing presidents of the other party and making it more and more difficult to pass anything. Frances Lee offered some interesting evidence that the Senate has become less about policymaking and more about messaging, as the percentage of Senate staffers hired to do communications work has gone from about zero to close to 50 percent over the past half century. We saw evidence that the Supreme Court has become more polarized and that the media are contributing to this as well. Boris Shor demonstrated that many (although not all) state legislatures are becoming more polarized, and I devoted my talk to showing how many reforms designed to lessen partisanship basically don't work.
Activists are increasingly organizing over a broader range of issues and they've become adept at getting political parties to adopt their stances, making it even harder for politicians to resist them.
As Hans Noel notes, there wasn't very much discussion about just what's driving this polarization, even if we observe it at all levels. Hans' argument is that it's being driven by ideological activists, who take over parties and compel elected officials to move further to the extremes.
I think this is an important point that is often missed in the discussion about polarization and ways to mitigate it. No one gets into politics with the goal of driving the parties further apart. (Well, almost no one; a 1950 APSA committee really did advocate that.) People get involved in politics usually because they want the government to do something different from what it's currently doing. Maybe they think it should be harder to obtain an abortion or a handgun. Maybe they think corporate taxes should be lower or we should abolish the death penalty or end a war. They know that their own individual effort isn't likely to change much, but maybe if they work alongside other people who share their views, or better yet convince a party to adopt their views, maybe they can convince some officeholders to change their minds, or replace them with new officeholders who don't need to have their minds changed.
Activists also generally recognize that politicians prefer to play it safe. That is, officeholders take the stances they take because they're trying to maximize their chances for re-election. So activists have to offer the politicians help (in terms of labor, endorsements, or money) to make up for the politicians changing their stance in a slightly less popular way, or they have to pose a threat (depriving them of labor, endorsements, or money) if the politicians don't change their stance. Only when the reward or threat is perceived as great enough to overcome the penalty a politician believes she will face for switching to a less popular stance will a change happen.
Activists have become better at this over time. They're increasingly organizing over a broader range of issues and they've become adept at getting political parties to adopt their stances, making it even harder for politicians to resist them. This isn't necessarily a bad thing. Indeed, this is how governing ideas are generated and translated into law. But it's important to remember that the parties aren't far apart because people hate each other; they're far apart because people want the government to do things. This is why exhortations for common ground tend to fall on deaf ears. People favor compromise in principle, except on the one thing that drove them into politics in the first place.
Just as polarization isn't really anyone's goal, de-polarization isn't much of a policy agenda. You can reform redistricting or open up primaries or organize a Senate Secret Santa program, but that won't change the fact that activists still want stuff, and they're the ones who appear to be in the driver's seat.