It'd be hard to deny that a wave is building; New Jersey and Virginia were only a taste of what's to come next year. But, even more important (at least in the long-term) is whether Democratic gains will be limited almost entirely to urban and suburban Congressional Districts or if it'll extend to rural ones as well.
Doesn't really seem like it if you go by the Virginia results. Obviously that is just one region though, and rural areas in other states could drift back a little to Democrats, but at least right now it seems like the party has a lot of work to do on that front.
Another significant issue is whether suburban areas becoming increasingly Democratic are primarily due to Whites with a college degree or more minorities living in the suburbs. Didn't Whites with a college degree constitute a higher share of the vote in Virginia's state elections than in 2016? Does anyone know if they voted more Democratic than in 2016?
If you go by the exit polls, Northam won Virginia by a larger margin than Clinton did last year largely because whites with a college degree supported him more than they did Clinton, and because they constituted a larger share of the vote.
https://www.washingtonpost.com/graphics/2017/local/virginia-politics/governor-exit-pollshttp://www.cnn.com/election/results/exit-polls/virginia/president%age of the Virginia electorate who are white / no college degree in 2016: 29%
%age of the Virginia electorate who are white / no college degree in 2017: 26%
%age of the Virginia electorate who are white / college degree in 2016: 38%
%age of the Virginia electorate who are white / college degree in 2017: 41%
2016 margin among whites without a college degree: Trump +47
2017 margin among whites without a college degree: Gillespie +46
2016 margin among whites with a college degree: Trump +4
2017 margin among whites with a college degree: Northam +3
