THIS YEAR'S political campaigns generated much regretful commentary about our polarized society, and those red-and-blue maps of the results reinforced the sense of a divided nation. But this polarization is at once milder and more serious than is often presumed. The good news is that ordinary Americans are probably less polarized than in the past. The bad news is that several powerful forces are pushing them further apart.

First, the good news. More voters on Election Day described themselves as moderate than as liberal or conservative. Many professed compromise positions on supposedly divisive issues: They were for gay civil unions, but not gay marriage; they opposed abortion, but with exceptions that allowed some room for choice. Academics who study opinion on issues such as school vouchers, the death penalty, immigration and equal rights for women find that attitudes in red and blue states are remarkably similar. It's true that regular churchgoers are mostly Republican and non-churchgoers are mostly Democrats, but about three-quarters of Americans fall in the middle -- they are somewhat religious and could go for either party. Some questions that appeared to split the nation a few years ago -- for example, affirmative action -- no longer are electoral wedge issues. Even the divisions over Iraq are mild next to the old divisions on Vietnam, when some not only opposed the war but sympathized with the enemy.

Next, the bad news. Although citizens are not deeply divided, the minority that dominates the political arena is genuinely polarized. A number of shifts seem to explain this. Television, once a force for unifying moderation when three networks ruled the air, is now the province of noisy cable shows that thrive by staging furious arguments. The Internet gives arguers an additional platform and a chance to form cyber-societies of like-minded folk who reinforce each others' indignation. The growth in political spending and in single-issue activism is fueled by ideologically impassioned donors, and their money encourages elected officials to take harder positions. Falling turnout in primary elections, particularly in congressional races in off years, cedes the field to fiery partisans. Between 1996 and 2002, turnout in congressional primaries halved from 34 percent to 16.8 percent, according to David C. King of Harvard University.

Most of these shifts are unstoppable, and some are even welcome. The flowering of political argument on cable networks and the Internet represents a welcome broadening of the public square, even though it renders it more caustic. Ideologically impassioned donors are preferable to the non-ideological sort, whose only motive in financing campaigns or setting up Washington lobbies is to extract pork-barrel favors. Nonetheless, the resulting polarization is worrisome. By reducing the space for bipartisanship, it can condemn Congress to gridlock. By driving elected officials to the fringe while citizens inhabit the center, it can alienate citizens from their government. Over the long term, moreover, the polarized minority may eventually succeed in polarizing the majority.

What is to be done? One major driver of polarization is not rooted in unavoidable change: This is the scandalous way in which electoral districts are drawn for the House of Representatives and state legislatures. The redistricting triggered periodically by the census has become an opportunity for party leaders to create politically homogenous districts that ensure incumbents' re-election and remove incumbents' incentive to represent the political center. Nobody wants to censor television or stifle citizens groups such as the Sierra Club and the National Rifle Association. But the incumbent protection racket in Congress is a different matter. It is offensive in itself, and the polarization of the nation's political elites provides a further reason to break it.