Why would SC have a lightning fast D trend while NC stays static? SC is supposed to be a big hub for retirees, while NC is supposed to be bringing in white liberals to Charlotte and the Research Triangle.
1. Plenty of white liberals come to SC for jobs. It isn't the same as Florida.
2. SC was pretty much always just on the edge of being competitive. In previous environments the votes just weren't there for Democrats to win but its always been one step away from becoming a battleground state. The truth is that it just isn't that Republican like Alabama and Mississippi are. Whether or not 2020 ends up being that one step has yet to be seen, but I wouldn't exactly call SC becoming competitive a "lightning fast" trend.