The Ohio senator seems to check all of Romney's boxes. But it's unclear how much of an asset he'd really be to the campaign.

As Mitt Romney's selection of a running mate looms, Rob Portman occupies a strange niche: He is the consensus prediction for the vice presidential nomination in the political class, but remains almost entirely unknown outside of Ohio.

The Ohio freshman senator seems to have surged to the front of the pack largely on the strength of anonymous Romney advisers saying that the candidate seeks "an incredibly boring white guy" to run with him. As if to prove that Portman was the man, BuzzFeed sought to create a list of "15 genuinely interesting things about Rob Portman," but fizzled after 11 or 12.

Just as with another of Romney's short-listers, Tim Pawlenty, a Portman pick would seem to reinforce the candidate's strengths, rather than try to complement him with a totally different set of skills. Like Romney, Portman is a numbers-and-business man. He spent years as a trade lawyer in Washington, then served in the U.S. House form 1993 to 2005. In 2005, he became U.S. trade representative and then a year later succeeded Joshua Bolten as director of the Office of Budget and Management. That knowledge of Washington -- including the ins and outs of both the legislature and the executive branch -- would be hugely helpful to Romney, who spent his entire career in business except for a term as governor of Massachusetts. Like Romney, his name is a byword for competence. And the Ohioan seems to be generally well-liked on both sides of the aisle. And McKay Coppins has argued that Portman would be, if not quite Marco Rubio, useful for outreach to Hispanic voters.

But despite the momentum in Portman's favor, he seems to have at least as many weaknesses as strengths. His Achilles' heel is his time in the Bush Administration. The Obama team has already begun to argue that Romney would simply reprise George W. Bush's policies, and a former Bush official on the Republican ticket would make it even easier. What's more, Portman oversaw the OMB during a particularly profligate time. The 2008 budget, the only one he oversaw, projected a budget more than twice as large as the 2007 budget. At a time when the Republican Party, under Tea Party influence, is preaching a particularly strong brand of fiscal restraint, a Portman nomination would undermine that message. On the other hand, it's worth noting that Portman won election to the Senate in 2010 despite the best efforts of his feckless opponent Lee Fisher to tie him to the Bush budgets.

Nor is it clear that Portman would aid Romney with his resume or his electoral abilities elsewhere. Portman brings a bit of overseas experience to the table from his days as trade representative, although that's a far cry from diplomatic or military experience. Theoretically, Portman he could help deliver Ohio, a key swing state, to Romney, but a Quinnipiac poll in May suggested that he wouldn't move the needle much toward the Republican in the Buckeye State.

Romney seems to choose aides whom he feels comfortable with and sticks with them regardless of outside criticism, so if he has a good rapport with Portman, he'll wave away these concerns. Opting for the candidate who gels well with the team over electoral expediency is a legitimate choice, but one that could come at a cost.