As of 2012, the divide was pretty wide. Half of all voters were living in a county that President Obama or Mitt Romney, the Republican nominee that year, won in a landslide, which is defined here as a county won by 20 percentage points or more.
The proportion of voters living in landslide counties has steadily increased since 1992, a trend that reflects the growing tendency of like-minded people to live near one another, according to Bill Bishop, a co-author of “The Big Sort,” a 2008 book that identified this phenomenon.
