The country is getting more geographically segregated along partisan lines, divided between heavily Republican areas and heavily Democratic areas. There are fewer competitive legislative and Congressional elections than there used to be, with fewer areas that are evenly split between Republicans and Democrats, and more areas that are either heavily Republican, or heavily Democratic. Is this because people are moving to areas where there are more people of their own political party? Or moving away from neighbors who have an opposing ideology?
No. A recent study finds that partisan segregation is not due to such sorting or migration. Counties trending Democratic tend to so because of generational change; Counties trending Republican tend to do so because of party switching by long-term residents.
The study explains:
between 2008–2020, we find that residential segregation between Democrats and Republicans has increased year over year at all geographic levels, from neighborhoods to Congressional Districts. Individual demographic information reveals that segregation increases for voters of most demographic backgrounds, but that Democratic and Republican trending places have starkly different demographic profiles, thus contributing to the growing confluence of demographics, partisanship, and geography in the United States. We further decompose the change in segregation into different sources. Increases in segregation have not been driven primarily by migration but rather by generational change, as young voters enter the electorate, causing some places to become more homogeneously Democratic, and by existing voters leaving the Democratic party and causing other places to become more Republican.
The study is titled “Causes and Extent of Increasing Partisan Segregation in the U.S. – Evidence from Migration Patterns of 212 Million Voters,” and is from the National Bureau of Economic Research.
