I would add to this that the Electoral College prohibits sectional campaigns. The Dems have been running such for a long time now, and it has made the country more divided. But if you look at the spread, the party wins the cities almost exclusively, and then tries to hang on as the midwest or country comes in. This balkanization has balkanized the party, and hence, the reason they are losing ever more. It will be tough for them to dig out of this hole and become a generalized party again, but they must to be competitive.
Still, read this.