Who is the most likely person to run for the Dem. nomination besides Clinton?

[Vosem]

O'Malley may run, he seems too committed not to, but he'll drop out before Iowa; if Mikulski retires it's easy for me to imagine him running for the Senate. Schweitzer and Sanders will run and compete in the early primaries; Schweitzer will represent discontent from the right of the party, Sanders from the left. I doubt either will win any primaries, but I can see both coming within single-digits, in IA and NH respectively. Clinton will have been openly campaigning for almost a year by early 2016; people will find things not to like. Of the two, I think Sanders has the better shot at carrying a primary or two, but he doesn't have the strength to win the nomination regardless of what happens. If Clinton were to crash for some reason and Schweitzer had been campaigning for some time, I could see him beating a late entry and becoming the nominee.