While three years away from the election....one might sit and speculate over how it might happen.
There are two ways that the Democrats can carry this election.
1. Using the Clinton method 1992/1996. Have a third-party guy standing there to take votes. In this case, you had Ross Perot existing in 1992 to help take 19-percent of the national vote from George Bush. This allowed Bush to only win 18 of the fifty states. Oddly enough, if you use the voting district map....this also allow Clinton to take roughly 40 to 45 percent of the districts (instead of using the state method).
In 1996, Perot is there again, to help Clinton win....this time by taking 8-percent of the vote. Without Perot, Bob Dole would have won.
The Jimmy Carter win? Well, this is interesting because Carter only took 23 states....to Ford's 27 states. Carter wins by 1.7 million votes. Carter's big upsurge was taking metropolitian votes (typically where Democrats are stronger), and virtually all of the south. Carter, four years later, in 1980....could NOT win metropolitan areas (go figure that one).
2. Using the Obama method 2008/2012. Twenty-eight states went for Obama in 2008. A lot of this upsurge was the ability to get blacks mobilized, registered and showing up to vote. The same trick was used in 2012. Having two GOP candidates that weren't exactly embraced by the entire Republican crowd....probably helped as well.
So, that's basically it....two methods to push the Republicans out. You either find the perfect third-party guy, or you go to a black candidate that draws mobilization/votes. Without Perot....Clinton never wins. Without a black background, Obama never wins.
If you look at 2020, it might be an interesting election.