should be able to look back and see some corresponding demographic trends. We ought to be able to take advantage of the fact that hindsight is 20/20 and find the shifts in population that corresponded to the balkanized communities we live in today. Our third test searched for demographic movements that differentiated Republican places from Democratic ones over the past thirty-six years.
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Test One: Does Like Attract Like?
For this test, we returned to the county-level presidential votes that had led us to our first story about political sorting and calculated how loyal each county had been to the two major political parties since World War II. Some counties (346, to be exact) had voted for the same party in every presidential election since 1948. In each election thereafter, another group of counties picked a side and stuck with it through the 2004 contest. Fifty-four more tipped in 1952; 536 tipped in 1968.
Before counties tipped, we found they were on average quite competitive. The difference between Republican and Democratic candidates over the years was just 2 or 3 percentage points in untipped counties. But here's the interesting part about the tipping phenomenon: once a county tipped, the spread kept growing. The average vote spread in presidential elections among tipped counties was hugeâan overwhelming 20 percentage points in most elections. This was particularly true for Republican counties, which saw the margins for Republican presidential candidates increase over time. In addition, once these counties tipped, they grew more partisan. The trend was stronger in Republican than in Democratic counties. We surmised that this difference was caused by the tendency of Democratic counties to attract a more diverse populationâmore ethnic minorities, more people born outside the United States, more young people, and more people with college degrees. (I will discuss all of this later in the book.)
We found that Republican counties tended to become more politically segregated than Democratic counties. * This happened in part because Republican migrants were unusually attracted to Republican communities. Between 1995 and 2000, 79 percent of the people who left Republican counties settled in counties that would vote Republican in 2004âand they were most likely to move to counties that would be Republican landslide counties. We don't know the politics of individual movers. We do know that when people left counties that would vote Republican in 2004, they were two and a half times more likely to move to other counties that would vote Republican than to those that would vote Democratic. By contrast, people who left counties that would vote Democratic in 2004 migrated to both Republican and Democratic counties without showing much of a preference for eitherâalthough they were unlikely to move to counties that would become Republican landslide counties.
As a result of this sorting, most counties were zooming off in partisan directions. Between 1976 and 2004, the gap between the parties increased in 2,085 counties; only 1,026 counties (33 percent) grew more competitive. California is the stereotypical "blue" state. But within California, 17 counties grew more Democratic after 1976, and 30 became more reliably Republican. Only 11 California counties (19 percent) became more closely contested. In 1976, 44 percent of San Francisco County's population voted for Republican Gerald Ford. Over the next seven presidential elections, the percentage of San Franciscans voting for the Republican presidential candidate dropped every four years. By 2004, just 15 percent of San Francisco's voters supported George W. Bush. San Francisco didn't become more Democratic because its population grew; the number of voters in San Francisco County hadn't changed since 1948. San Francisco was transformed because Democrats sorted themselves in and Republicans sorted themselves out. Orange County was always Republican. But despite a