Even with Jon Huntsman dropping out and endorsing Mitt Romney on Monday, it's too soon to declare Mitt the Republican nominee. But as Romney battles with his remaining rivals for enough delegates to clinch the nomination, "another, far less formal and far more secretive campaign is getting under way," says Reid Wilson at National Journal: The race to be named Romney's running mate. "The veepstakes is one of the great political parlor games, an exercise both fascinating and overrated," says Howard Kurtz at The Daily Beast. And Romney actually started the VP speculation a tad prematurely himself last July, so nobody should begrudge us having "some fun thinking about it." Here, seven names that show up on the short list, and why:

1. Marco Rubio
Florida's freshman senator seems to be at the top of every VP-watcher's list. Mike Huckabee, a 2008 VP short-lister himself, summed up Rubio's advantages in an interview with Newsmax: "Great ties to the Hispanic community, an amazing communicator, a terrific leader," and a popular figure in Florida, "a very key swing state." Rubio would also add a jolt of excitement to a bland Romney ticket, and he's "acceptable to every faction within the GOP: The Tea Partiers, the establishment, and social conservatives," says Eliza Gray at The New Republic. But he's only been in the Senate a year, and he's untested on the national stage. Oh, and he's repeatedly and "emphatically said he is not going to be the VP nominee."

2. Chris Christie
New Jersey's pugilistic rookie governor is a GOP star, and he's "been campaigning hard for Romney," says The Daily Beast's Kurtz. His "passion and blunt talk" would be a good complement to a nominee "who often sounds like a cold-blooded management consultant." On the other hand, "his big mouth would undoubtedly get Romney into trouble," and as a social moderate from the Northeast, Christie wouldn't bring much to the table in terms of geography or evangelical outreach. Still, it could be like Bill Clinton picking fellow Southern Democrat Al Gore in 1992, which worked, says Josh Kraushaar at National Journal. As Romney's No. 2, Christie would "excite the base and serve as an effective attack dog against Obama, but without alienating independent voters."

3. Rob Portman
The first-term senator from Ohio "satisfies many of the criteria one would want in a vice president," says The New Republic's Gray. With six terms in the House and stints as George W. Bush's budget chief and trade representative, Portman has "enough experience to credibly argue that he's qualified to be president." He's also well-vetted, hails from a key swing state, and is "a favorite among establishment conservatives." Picking Portman "would be consistent with the Romney campaign's play-it-safe strategy," says National Journal's Kraushaar. But what the Romney ticket needs is excitement, and Portman doesn't have "a whole lot of charisma." 

4. Rick Santorum
The former senator who tied Romney for first in Iowa would be my top VP pick, says Don Surber at the Charleston, W.V., Daily Mail. "He's a solid social conservative who is the party's best chance at picking up Pennsylvania," Santorum's home state. He would also help win the Midwest, and "he can handle the worst the media will dish out." Santorum "has a certain blue-collar appeal" that Romney conspicuously lacks, says The Daily Beast's Kurtz. But he's also "a long-winded campaigner," and his extreme social positions could turn off moderates and independents.

5. Tim Pawlenty
The former Minnesota governor, who dropped out of the race in August 2011, is also plausibly "blue collar," and could help the "quarter-billionaire private equity titan" win over "Rust Belt voters in Ohio and Wisconsin," says Alec MacGillis at The New Republic. And whereas a big personality like Christie would upstage Mitt, Pawlenty is "even more lackluster as a speaker than Romney," making Romney "seem positively dynamic by comparison."

6. Nikki Haley
South Carolina's governor gave Romney a key early endorsement, and unlike Pawlenty, Haley "is a polished performer," says Kurtz. She would help Romney build bridges to women and true-blue conservatives, and as "the first Indian-American on a national ticket," Haley would lend some historical gravitas to a bland nominee. But she hasn't been vetted, says National Journal's Kraushaar. Picking Haley would "amount to a Sarah Palin–like strategy for Romney — choosing someone who looks terrific on paper, but who could cause the campaign unexpected headaches."

7. Susana Martinez
"The biggest surprise from my conversations [with GOP insiders] was that Martinez's name came up almost as often as Rubio's," says Gray at The New Republic. Like Rubio and Haley — and Palin — the first-term New Mexico governor is "untested on the national stage," but having a Latina on the ticket would help Romney win Latino-heavy Western swing states like Colorado, Nevada, and Martinez's New Mexico. Martinez has raised some eyebrows by attending several Republican National Committee meetings, "an unusual effort for someone so new to office," says National Journal's Reid. But for what it's worth, "Martinez told a local newspaper reporter last week she isn't interested in the job."