That's why I think that Romney needs to pick Ohio Senator Rob Portman as his running mate. Portman is a safe pick, and the popular Senator has an impressive resume filled with Executive Branch and Legislative Branch experience.
A former member of the U.S. House, Portman served as Trade Representative for the U.S. before being scooped up by George W. Bush to run the Office of Management and Budget. Portman's terms in those office are more of a liability for him in his own base rather than perhaps with independents. Portman is more moderate and aligns himself with the political temperament of George H.W. Bush.
Beyond all of this, Romney MUST win Ohio. I think Romney can win Florida without picking Marco Rubio, and he can win New Hampshire on his own given his popularity in the state. If he concentrates on those two states and holding the other states he should win, that gives him a path to 270 votes. In fact, under my analysis, Romney winning Ohio and New Hampshire would swing the election to him by the final electoral total of 270-268. Ohio has 18 Electoral Votes and New Hampshire has four.
Of course, this also assumes Romney is able to hold onto a slim lead in North Carolina and break a polling tie with Obama in Virginia.
Portman, I think, if Romney is thinking a Vice Presidential candidate can swing a state, is probably his best bet to help him to 270. He, of course, may not be thinking in this direction.
The wind is still at President Barack Obama's back, though. He leads in the important battleground states, but the specter of a worsening economy could definitely change things over the next 98 days.