Why has North Carolina and Virginia trended Democrat 4 times in a row now?

[Nyvin]

The entire southern east coast from Atlanta up to DC seems to be developing into a second BosWash area.   The Metros are among the fastest growing in the country and it's increasingly developing a "digital economy".   

South Carolina doesn't have any large metro to drive this change so it's going slower than the other three.

This is distinct from Florida where the main drivers to change are Latino immigration and Retiree migration. 

[Nyvin]

Didn't Obama slightly underperform in California in 2012 compared to 2008?

I think he underperformed in all 4 of them.  They all still trended Dem though.

[Nyvin]

...also in regard to Virginia vs North Carolina,  don't forget the Republicans were successful in implementing their voter suppression law in North Carolina for 2016.

[Nyvin]

Both states are becoming more urbanized and more educated, though Virginia is becoming more Democratic faster because of the high density of Federal workers in NoVa. North Carolina is a bit more like Florida in that its population trends are somewhat canceling each other out, though the Dem trend is slightly faster.

Florida is becoming more and more Republican and has been doing so for years.

Obama won Florida twice...and from 2012 to 2016 Florida's PVI went from R+3 to R+2.   

I'm not saying it's trending Dem,  but the political future of Florida is impossible to predict.