As I see it there are two ways back to the 50 state campaigns of the mid-20th century:
1. The rise of a religious left, which allows Democrats to seriously contest the Evangelical vote, forcing the GOP to expand its coalition and making the Deep South competitive again. A Great Awakening style revival historically follows the kind of economic turmoil the country has recently faced, and the movement would probably have a progressive bent given today's youth.
What kind of religous left would that be? Economically left ("share with the poor"), environmentalist ("preserve god's creation"), globalist / pacifist ("peace to the world"), or even social?
More importantly, this says something about American politics. Making the whole nation competitive is predicated on the rise of a new religious movement?