Apparently, it's Jon Huntsman. Via US News & World Report's Political Bulletin:
US News Weekly, in its Washington Whispers column, reports, "When it comes to 2012, there's no potential Republican opponent who makes" former Barack Obama campaign manager David Plouffe "shake in his shoes," though Utah Gov. Jon huntsman (R) makes him a "wee bit queasy." Plouffe says, "I think he's really out there and speaking a lot of truth about the direction of the party."
This is, in my opinion, a pretty noteworthy thing. Plouffe was the architect of a campaign that I have tremendous respect for, having worked on the opposing side of it last year. If Huntsman worries him, even a little, that's something I'd say is a big endorsement for Huntsman as a could-be 2012 contender, and something that sets him well apart from the rest of the (presumptive) field.
Now, I know conservatives who don't like Huntsman much. I must admit, I'm a little confused as to why, when some of those who I've heard express a dislike for him are people who say they prioritize fiscal concerns above all else and Huntsman got a 60/B rating from CATO last year on their fiscal report card-- a better score than all but four governors out of 46 assessed-- and a 59/B rating from CATO in 2006-- again a better score than all but four governors out of those assessed. These conservatives will probably try to argue that Plouffe saying that Huntsman is speaking "a lot of truth about the direction of the party" is a way of Plouffe saying he agrees with Huntsman, philosophically, or that Huntsman is somehow one of those who's a party-attacker, as opposed to a party-builder.
I don't agree with that at all. Huntsman has voiced some criticism of the GOP leadership, and he has staked out some positions on issues like the environment and civil unions that are different from those that many in the base of the GOP hold (something that is often read in and of itself by conservatives as an implicit criticism of them). But ultimately, Huntsman is a conservative with some slightly different opinions on a couple of things that I think could enable him to expand the GOP tent in a way that a lot of other potential 2012 contenders could not. His interest in the environment, support for family (even if not family in the conventional, heterosexual partnered sense of the word), and commitment to fiscal discipline (at least if you go with what CATO has to say on the subject) seems pretty similar, actually, to David Cameron-- the UK Tory leader who I voted for as party leader back in 2005, and who has totally revolutionized the party and put Labour in a bind. That's something I'd love to see the GOP do to Democrats right about now, and Huntsman might just be the man for it.
UPDATE: Ben Smith notes that Plouffe has clarified that he did not in fact make the "queasy" comment cited above. Sounds like the rest is all him, though. [intro]