Nate Cohn posted this map of the South (Clinton vs. Sanders):
He notes that OK, NC, and FL all have party registration, and so the "Dixiecrats" (or whatever you want to call them) are unable to crossover and vote in the Republican primary.
Not necessarily a perfect correlation there: Louisiana has party registration, too, and the biggest D registration advantage out of all of those states to boot. Furthermore, look at the areas surrounding western NC (North GA, East TN, SW VA, etc) where there isn't party registration - Sanders came within single digits in about 20 counties in North GA and did quite well in East TN and VA, too.
Adam Griffin, that's a fantastic signature.
