The problem, as I see it, is that the middle of the country is slightly (or maybe a little more than slightly) right of center, based on the definitions that were used when we were younger. For Democrats to win on a national level, they need a candidate with exceptional qualities, like Obama or Bill Clinton, who can pull a coalition together.
Or they need Republicans to nominate someone so awful, so utterly lacking in moral character, that even LIZ CHENEY can't stomach him.