Sam Smith - Hillary Clinton lost about 60% of the states in the last election. Part of this was her fault but part was because of a cultural split in America between places like Kansas and New York, which the Democrats continue to fail to deal with.
Clinton came across as a classic east coast elite liberal unlike her husband who broke into national politics in part because he came across as a bright southern governor. Listening to MSNBC talkers boosting Elizabeth Warren and Cory Booker brought to mind that this division still exists. This doesn't mean that Warren - although not Booker - might not well be one of our best president ever, she still has to get elected first.
Democrats should be turning their eyes instead to possibilities from more conventional America. One example would be Tim Kaine from Virginia, one of the country's most consistently popular politicians, who gets an 80% voting score from the liberal Americans for Democratic Action. Not perfect, but it's better to have a 80% good candidate who wins than a 100% good one that can't.