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

[Mr. Morden]

Hillary Clinton is presumably the most likely person to run for the 2016 Democratic nomination for president, since most of the rest of the field would likely sit out if she doesn't run.

But who's the second most likely person to run?  Not the second most likely to win the nomination, but the second most likely to run for the nomination?

At this point, I'd actually have to go with Sanders.  Since Clinton now seems pretty likely to run, the question is largely "who would still run if Clinton's in the race?".  O'Malley is virtually a lock to run if Clinton bows out, but I don't think he's going to go through with it if Clinton's in the race.  Same for Biden, Klobuchar, etc.  Schweitzer is a possible candidate even if Clinton runs, but I think Sanders is more likely at this point.

[This question obviously excludes no-name non-entities like Vermin Supreme and the like.]

[Mr. Morden]

I remain very curious to see if Clinton will agree to debate Sanders (should he be her lone challenger).  And in general, how well he would do.  Of course he's not going to win the nomination, but Clinton (like any frontrunner) will inevitably have a bad week, a gaffe, whatever.  If Sanders is her only challenger he'll get at least some play, and he'll be the face of any discontent with Clinton within the party (and there will surely be *some*).  It's unclear how far he can go with that.  Clinton is still the favorite in all 50 primaries, but Sanders would inevitably do better than the 1% or whatever he's polling at now.

[Mr. Morden]

If Schweitzer was allegedly scared out of running for Senate because of some opposition research against him (which, according to some Politico article even DSCC staff feared would make him unelectable in Montana), then why is he still running for President? Won't the dirt just come out in this race?

That assumes that the reason for him skipping the Senate race is because of said oppo research, as opposed to him simply not wanting to waste his time on a Senate race when he'd rather run for president.