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It's not a new phenomenon. Bill Bishop, who inspired The Rural Blog, wrote in the 2008 book, The Big Sort: Why the Clustering of Like-Minded America is Tearing Us Apart, that people increasingly flock with others who share similar socioeconomic profiles and politics, leading to rural areas becoming more conservative and cities more liberal.
The rural-urban divide has continued to grow, as evidenced by the 2016 presidential election, where Donald Trump was overwhelmingly popular in rural areas, while Hillary Clinton won most of the major urban areas. Wasserman notes that "61 percent of voters cast ballots in counties that gave either Clinton or Trump at least 60 percent of the major-party vote," up from 50 percent in 2012 and 39 percent in 1992.
"Of the nation’s 3,113 counties (or county equivalents), just 303 were decided by single-digit margins—less than 10 percent," compared to 1,096 in 1992, "even though that election featured a wider national spread," Wasserman writes. "During the same period, the number of extreme landslide counties—those decided by margins exceeding 50 percentage points—exploded from 93 to 1,196, or over a third of the nation’s counties."
"Between 1992 and 2016, the share of voters living in extreme landslide counties quintupled from 4 percent to 21 percent," Wasserman writes. While communities can change allegiances, Wasserman notes that "most places just aren’t budging—in fact, they’re doubling down. In an increasing number of communities like Baldwin County, Alabama, which gave Trump 80 percent of its major-party votes, and San Mateo, California, which gave Clinton 80 percent, an entire generation of youth will grow up without much exposure to alternative political points of view. If you think our political climate is toxic now, think for a moment about how nasty politics could be 20 or 30 years from now." (Chart: Major-party presidential candidates have increasingly won more counties by larger margins)