The South is the fastest-growing region of the country, and Democrats are hoping that a flood of Northern expats and demographic change will allow them to turn red states to blue at a fast enough pace to counter the region’s growing share of the Electoral College.

Democrats have already made big gains in some Southern states, like Virginia and Florida. But Republicans have held firm or even made gains of their own in other states, including Texas, a state where demographic and migration trends seem as if they should be helpful to Democrats.

The explanation for the varied pace of Democratic gains in the South, along with the transformation of Dixie more generally, is illustrated with census data compiled by my colleague Rob Gebeloff for The Upshot’s project on migration.

The data shows that the scope and sources of population growth vary considerably across the South. The migrants moving to Tennessee and Texas bear little resemblance to those moving to Virginia or Florida, and Democrats will struggle to make similar gains so long as that’s the case.