The 2017 Census local population estimates, released this morning, show that Americans are moving from blue counties to red counties, and at a quickening pace. The flow of people from blue to red counties has picked up in recent years, steadily increasing since 2012, and the exodus is greatest in dark-blue counties—those where Hillary Clinton beat Donald Trump by more than 20 percent. (Blue and red refer to whether Clinton or Trump got more votes in 2016; dark and light refer to whether the marg…