If I may go English professor on you all, here's the bottom line: There is an American narrative. It's an optimistic story about people's escaping the rigid classifications of other societies and having the freedom to improve their lives, worshipping the God of their choosing and living at peace with your neighbors. And people believe it.
The party that habitually wins is the one that understands that story the best. Since Reagan in 1980, the GOP has controlled the narrative. Clinton only won by understanding the American narrative and explaining better how he fit in. The Dems too often seem more interested in deconstructing the narrative (or substituting it) than telling the next chapter. That is to say, they sometimes seem more interested in revising our understanding of the past than in dealing with the present, or telling an entirely different story.
The Dems need a new storyline. They need to connect to the American narrative.