Vote Like Thy Neighbor: Political Polarization and Sorting

The buzz these days is that American politics may be entering a “postpartisan” era, as a new generation finds the old ideological quarrels among baby boomers to be increasingly irrelevant. In reality, matters are not so simple. Far from being postpartisan, today’s young adults are significantly more likely to identify as Democrats than were their predecessors. Along with colleagues at the Brookings and Hoover institutions, we recently completed a comprehensive study of the nation’s polarization. Our research concludes not only that the ideological differences between the political parties are growing but also that they have become embedded in American society itself.

Large events made some increase in polarization inevitable. In the wake of the Vietnam War, the post-World War II foreign-policy consensus collapsed. Less than a decade after President Nixon declared that “we are all Keynesians now,” stagflation and soaring interest rates spawned the controversial tenets of supply-side economics. Social movements and the Supreme Court put long-suppressed, highly divisive cultural issues back on the public agenda.

But polarization has proceeded even further than these shifts made necessary. The great majority of voters now fuse their party identification, ideology and decisions in the voting booth. The share of Democrats who could be called conservative has shrunk, and so has the share of liberal Republicans. The American National Election Studies asks voters a series of issues-based questions and then arrays respondents along a 15-point scale from -7 (the most liberal) to +7 (the most conservative). These data indicate that 41 percent of the voters in 1984 were located at or near the midpoint of the ideological spectrum, compared with only 28 percent in 2004. Meanwhile, the percentage of voters clustering toward the left and right tails of the spectrum rose from 10 to 23 percent.

Most strikingly, political polarization has become akin to political segregation. You are less likely to live near someone whose politics differ from your own. It’s well known that fewer states are competitive in presidential races than in decades past. We find similar results at the county level. In 1976, only 27 percent of voters lived in landslide counties where one candidate prevailed by 20 points or more. By 2004, 48 percent of voters lived in such counties.

What accounts for the decline of ideologically mixed localities? Bill Bishop, a journalist, and Robert Cushing, a sociologist, who have studied this issue, stress that the age of “white flight” to the suburbs is over. Instead, during the past two decades, many whites have moved to one group of cities and many blacks to another. Meanwhile, young people have deserted rural and older manufacturing areas for cities like Austin and Portland. Places with higher densities of college graduates attract even more, so that the gap between such communities and less-educated areas widens further. Zones of high education, in turn, produce more innovation and enjoy higher incomes, generating communities dominated by upper-middle-class tastes. Lower-educated regions, by contrast, tend to be more family-oriented and more faithful to traditional authority.

Not surprisingly, this demographic sorting correlates with a widening difference in political preferences. What’s more, according to Bishop and Cushing, once a tipping point is reached, majorities tend to become supermajorities. This is consistent with the findings of recent political science and social psychology: individuals in the minority of their group tend to shift their views toward the majority, while members of the majority become more extreme in their views. In such circumstances, discussions within groups often intensify, rather than moderate, the underlying polarization.

Our study shows that this geographical sorting worsens polarization in several ways. When counties become more homogeneous, it becomes harder to use redistricting to create more competitive Congressional districts. (Recent research indicates that gerrymandering accounts for, at the very most, one-third of noncompetitive districts in the House of Representatives.) When states become more homogeneous, presidential campaigns begin by conceding a large number of contests to the opposition, disheartening their supporters in those states and increasing the majority’s electoral advantage. Polarization feeds on itself.

Because politics is a contact sport, hard-hitting partisan competition is unavoidably part of the game. A party system that differentiates sharply between alternatives has virtues, not the least being that it engages more voters, offers clearer choices and enhances accountability. But hyperpartisan politics also do damage, not least to public trust and confidence in government — and many Americans understandably yearn for less polarization. Because the underlying structure of our politics remains so deeply divided, the 2008 election may not requite their wish.