https://www.sciencedaily.com/releases/2019/11/191127121237.htm

In a study of county-to-county migration patterns in the U.S., the researchers found that when people migrate, they tend to move to other counties that reflect their political preferences. They added that the pattern also suggests that people moving from moderate partisan counties are just as likely to move to extreme partisan counties as they are to move to other moderate counties. However, people who live in a politically extreme county are significantly likely to move to a similarly extreme county.

This type of political sorting might turn extreme counties into "magnets" that pull people from moderate counties and exchange them with other extreme counties.