Democrats were able to become competitive so quickly in states like Virginia and North Carolina because they combined a growing nonwhite share of the electorate with gains among white voters, particularly in postindustrial metropolitan areas full of Northern expats. Without additional gains among white voters, Democrats will be forced to wait a long time for the children of foreign-born residents to carry them to competitiveness in Texas, a state that Mr. Obama lost by 17 points in 2012, and where there isn’t a flood of Democratic-leaning voters from New York to bail them out.
The political dimension of this is clearly on everyone's mind. It varies from state to state depending upon the number of northerners (who tend to be Democrats) moving into the southern state, and on the pace of immigration, since the children of immigrants are US citizens who are more likely to become Democrats than Republicans, but they have to reach voting age for that to make a difference. This is happening sooner in states like Georgia and North Carolina than in some of the other southern states.