Will the South ever go Democratic & the North Republican again?

[Beefalow and the Consumer]

Interestingly, Maryland and Delaware make up 13 electoral votes. While D. C. is clearly culturally northern, Maryland and Delaware have a mix of culture. Not counting them it's an even 190-190 split.

Maryland is predominantly Baltimore, Baltimore suburbs, and DC suburbs.  The remainder of the state is Appalachian, dairy farms, a bit of Amish country, military establishment, and coastal tourism.  The only part of Maryland that is truly "Southern" consists of the tidewater and southern rural portions.  And since they quit producing tobacco when I was a kid, those areas have lost their Southern character as well.  Given county populations, I estimate the state is made up of the following:

BosNyWash: 52%
Northern exurb/rural: 20%
Military: 10%
Southern rural/tidewater: 12%
Appalachia: 5%
Coastal: 1% (not counting tourist population)

All in all, a state I would characterize Maryland as over 80% Northeastern.  Or maybe put another way: 75% Northeast, 25% Virginia.

As for Delaware, about 60% of the population is part of the Philadelphia metro, and the rest is dominated by coastal tourism.  Basically a southern extension of the Jersey Shore.

[Beefalow and the Consumer]

To answer the question of whether the South will go Democrat and the North Republican:

One of the big trends happening right now is the leftward swing of the Sunbelt suburbs (and suburbs in general).  Southern, affluent, white suburbia was the "New South," which was as big, or a bigger reason for the South's move to the GOP as was the backlash to the Civil Rights Movement.  Matthew Lassiter examines this in his most excellent book, The Silent Majority: Suburban Politics in the Sunbelt South.

Trump and Sanders both demonstrate a significant backlash against the economic and social elite that the Democrats have come to represent.  Can those elements coalesce into a single party?  This seems unlikely to me, but who knows?

[Beefalow and the Consumer]

A more populist GOP isn't necessarily a bad thing for the party (especially when you consider the long-term electoral prospects), but you need a Republican who can appeal to Northern Whites AND minorities.

The main problem with GOP populism is that it's easily outflanked but Democratic populism.  The GOP "populist" line against the Democrats is that they represent a social and technocratic elite who want Americans to lose.  The only people that message really resonates with are white.

Meanwhile, the Democrats easily capture the populist mantle by claiming GOP policies favor the rich, favor men, and favor whites.  This strategy doesn't do much for a large portion of white men, but demographic trends are making it easy to win elections with less than 40% of the white male vote.