1) Warren, if she takes the next four years to really emphasize her OK roots/be less of a Progressive for MA and more of a Progressive Populist for the whole country.
2) Warren if she doesn't do that.
3) Climbing Maggie to give TNVol an aneurysm
4) Bernie
5) Chris Murphy if he ever focused on his really excellent foreign policy and trade positions and less on guns (but he won't and doesn't... *sigh *)
6) (hypothetical)Governor Troy Jackson? It would be kinda weird since he would have been a State Senator a mere four years before running, but I REALLY like him.
7) Kamala Harris TBD. Warren likes her a lot, which is a point in her favor, but I'd have to see what she'd do. I'm also somewhat skeptical of 1st term Senators becoming POTUS.
Honorable mention goes to Sherrod Brown, but I A) think he has a 0% chance of running B) never focuses on building his national brand because of (A)
@White Trash -- I'll have to see more from JBE. I'm not in love with the fact that he's (fairly) socially conservative, but I could get over that.
He's been running a fairly leftist (relatively for a Louisiana governor) administration. He's only emphasized his SoCon credentials and "family values" shtick on the issue of abortion.