Political division multipliers

President Bush’s margin last year over Sen. John Kerry of Massachusetts, 2.4 percentage points, was the smallest of any victorious presidential incumbent in history. He won a very close election.

But in most of the country, the 2004 race wasn’t even close to being close. A Pew Research Center analysis shows that in the majority of the nation’s 3,153 counties, the election was a landslide — with either Mr. Bush or Mr. Kerry winning by a margin of at least 20 percentage points.

Never before in modern times has so competitive a national election been the sum of so many uncompetitive parts.

Some have dubbed this “the big sort.” It’s not a new political phenomenon, but it’s more striking than it once was. In the two other very close presidential elections of the past half-century — 1960 and 2000 — fewer than half the nation’s counties (44 percent and 45 percent, respectively) were decided by a margin of 20 percentage points or more. Last year, the number rose to 58 percent.

Unlike congressional districts, whose lines are redrawn every decade (often to create safe seats for incumbents), counties’ geographic boundaries rarely change. So if it’s not redistricting, what is it that sorts the electorate into partisan enclaves? Some leading theories:

(1) It’s all about lifestyles. Everyone knows the stereotypes: Red Americans like barbecue, NASCAR and George W. Bush. Blue Americans go for Thai food, beat-up Volvos and anybody-but-W. With red and blue in such different universes, it’s hardly a surprise they would gravitate toward different neighborhoods.

But wait a minute. People have liked living among people like themselves since the dawn of civilization. Why would this have more of an impact now on voting patterns?

One hypothesis is that, as the modern communications revolution has promoted ever more well-defined lifestyle groupings (each with its own cable channel), social identity plays a greater role in determining where people live as well as the candidates and parties they support.

Last year the Bush campaign did a great job organizing around affinity groups. They identified potential supporters by the magazines they read, the television shows they watch, the beer they drink — to say nothing of the churches they attend — and used this to support a sophisticated get-out-the-vote effort.

But when political scientists look at public opinion survey data, they consistently find what matters most in determining partisanship is not who you are but what you believe.

For example, married, religiously observant Southern white men are among the most Republican voting blocs, leaning Republican by a margin approaching 3-1. But members of this bloc with liberal policy preferences, they lean Democratic by 2-1.

The same is true for all major groups (except African-Americans): Ideology trumps social identity by decisive margins as a predictor of partisan affiliation.

(2) OK then, it’s all about ideology. Republicans are more consistently conservative than they once were; Democrats more consistently liberal. Scholars who have analyzed survey data find the correlation between ideology and partisanship has increased by about one-third in the last generation.

Still, this doesn’t by itself explain the growing congruence between geography and partisanship. Only in looking at the shift’s regional basis does the picture come into sharper focus.

The most significant change in voting trends in the past half-century has been the realignment of the South from Democratic to Republican. White Southerners are no longer voting the way great granddaddy shot in the Civil War. They’re supporting the party more in sync with their conservative values and beliefs — and by doing so, have brought more ideological and geographic coherence to the electoral map.

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