Americans like to live in diverse communities. At least, that's what they say.
About two in three Americans say they prefer to live around people belonging to different races, religions and income groups. In reality, however, survey research shows that people are increasingly clustering together among those who are just like themselves, especially on the one attribute that ties the others together " political affiliation.
Nearly half of all Americans live in "landslide counties" where Democrats or Republicans regularly win in a rout. In the 2008 election, 48 percent of the votes for president were cast in counties where President-elect Barack Obama or Sen. John McCain, R-Ariz., won by more than 20 percentage points, according to the Pew Research Center.
The clustering of Democrats in Democratic areas and Republicans in Republican areas has been intensifying for at least three decades: In 1976, only about a quarter of all Americans lived in landslide counties. In 1992, a little more than a third of America was landslide country.
This week, as the nation memorializes the Rev. Martin Luther King Jr. and a biracial president takes office for the first time, it is easy to forget that America is not really a land united as much as two disparate lands that happen to live in the same country: A third of both Obama's and McCain's supporters have said they "detest" the other guy.
A consequence of such polarization is that large numbers of Americans no longer have much contact with people belonging to the other party. Many feel the views of their political opponents are not just wrong but incomprehensible.
"Americans tell survey researchers they prefer to live in diverse communities, but this country's residential patterns suggest otherwise," said Paul Taylor, who directs the Pew Research Center's Social and Demographic Trends Project. The question is why.
"Do some people gravitate toward communities so they can be among neighbors who share their political views?" Taylor and his colleague Richard Morin asked in a recent report. "Alternatively, does living in a politically homogeneous community diminish people's appetite for diversity?"
Sociologists have a term for this birds-of-a-feather-flocking-together phenomenon: Homophily. Some explanations for America's political homophily suggest that a president who is determined to be a uniter might be able to help the nation reverse course; other theories suggest that the forces of polarization are beyond the powers of any individual to influence.
Sociologist Michael W. Macy at Cornell University argues that political homophily is largely the result of network dynamics: Neighborhoods coalesce around certain viewpoints because people don't want to feel at odds with those around them. As views in a neighborhood become more homogenous, outliers feel like outcasts. They move if an opportunity arises, leaving their old neighborhood less politically diverse.
Another explanation for America's polarization offers more room for a president " especially a biracial leader such as Obama " to be a uniter.
Robert Huckfeldt, a political scientist at the University of California at Davis, says America's divide stems from Democrats' decision to throw their weight behind the civil rights movement. That turned the Republican Party into a largely white and Southern institution " about 90 percent of Mississippi whites, for example, vote Republican, while 90 percent of Mississippi blacks vote Democratic. Nationwide, Democrats have not won a majority of white votes in a presidential election since 1964.
"The racial polarization of politics is reversible, depending on the nature of the appeal," Huckfeldt said. "One might usefully contrast the appeal of Jesse Jackson in his presidential campaigns of the 1980s with the appeal of Obama and his candidacy. Without denying the importance of race, Obama has intentionally focused on unifying themes."
Bill Bishop and Robert G. Cushing, authors of "The Big Sort," a book exploring the causes and consequences of America's political polarization, offer a third explanation: People don't choose neighborhoods because of political yard signs; they choose neighborhoods based on their lifestyles " and lifestyles have come to determine Americans' political choices.
On a talk show in Minneapolis, for example, three people once told the authors they knew they were living among political opponents when they saw neighbors using lawn chemicals.
"These are the kinds of differences that are political in America today," Bishop and Cushing said in an e-mail they composed together. "People don't see themselves as members of demographic groups " a white working-class man, an educated woman. Like the woman in California who described herself to us as an `ocean-oriented person,' Americans define themselves by their interests: the bands they listen to, the foods they eat, the sports they follow, the spiritual beliefs they adopt."
Political polarization, according to this explanation, is a consumer phenomenon: You like Cheerios; I like Wheaties. Americans have lots of choices " you can live in a cul-de-sac surrounded by fellow Mormons, or in a gay enclave, or in a neighborhood where yoga studios outnumber fast-food outlets.
Lifestyle choices, in turn, determine political loyalties as voters search for candidates who feel like "one of us."
"The goal of a political campaign these days isn't to transform the electorate but to reflect back onto voters a picture of themselves " to make people think a vote for Bush or Obama is really a vote for themselves and their community," Bishop and Cushing said.
This might explain the loathing many Republicans and Democrats feel for each other. It isn't about taxes or terrorism: The yoga people simply can't stand what the lawn-chemical people represent, and vice versa. This might explain why, despite all of Obama's calls for an America that is larger than its differences, political polarization at the county level intensified between 2004 and 2008.
Marketers have long known that appeals to lifestyles sell products. Volvos and pickup trucks are more than just vehicles " they say something about who we are. In the age of Facebook, it appears that we no longer pick presidents because of their policies but rather because the candidates we choose allow us to advertise our own identities to the world.