Americans aren't moving to be around others who agree about single-payer health plans or the proper response to a nuclear Iran. We seek out comfort among people who live like we do, think like we do, act like we do. On Election Day, we tend to vote like our neighbors, and so it looks like we have sorted ourselves intentionally into Republican and Democratic enclaves, but those divisions are more about lifestyle than policy.
That's why the primary race between Barack Obama and Hillary Clinton was just as geographically polarized as the contest between John Kerry and George Bush. In 2004, half the voters in that very close election lived in a county where either Kerry or Bush won by more than 20 percentage points. In the dead-even 2008 primary, exactly half the voters lived in counties where Barack Obama or Hillary Clinton won by a landslide.
Democrats in '08 were evenly split along the same geographic lines as those that evenly split Republicans and Democrats in 2004. The better George Bush did in a county, the more votes Hillary Clinton won. The map of voting results by county in Missouri from the 2004 general election looks exactly like the map from the 2008 Democratic primary. Obama won the Kerry counties; Clinton and Bush won the rest.
The race between ideological opposites in 2004 had the same geographic divisions as the race between Obama and Clinton, who are ideological twins.
When this phenomenon was first discovered early in the primary season, there was a brief behind-the-scenes debate. The Clinton people thought this was proof that their candidate would be able to pull Republican votes in the fall. The Obama camp dismissed the comparison. You can't extrapolate primary results to the general election, they said. Two different kettles of fish.
The Clinton people looked at these results and began to change the campaign's itineraries. For the next several months, Bill Clinton spent most of his afternoons speaking from the back of a pick-up parked in the courthouse square of some red county. Obama, meanwhile, rolled up big leads in the cities. (He won the southern metro areas by the same margins that Hillary Clinton took Appalachia, though we didn't hear much complaining or surprise about those lopsided victories.)
The primary ended with the Democratic Party just as divided as the nation was in '04 and in exactly the same way.
Sen. Obama is stuck. He didn't find a way across the boundaries of lifestyle and culture that split Democrats. And now it's the middle of September, and he still is trying to find a way to bring these very different Americas together. (It might be that there isn't one.)
John McCain may have come to another conclusion: that he doesn't need to widen his net and can win by turning out the same voters who elected Bush. More on that shortly.