Mitt Romney (left), the presumptive Republican presidential nominee, and Rep. Paul Ryan, his running mate, arrive at a campaign rally in Mooresville, N.C., at the NASCAR Technical Institute on Sunday, Aug. 12, 2012. (Associated Press)

Mitt Romney (left), the presumptive Republican presidential nominee, and Rep. Paul Ryan, his running mate, arrive at a campaign rally in Mooresville, N.C., at the NASCAR Technical Institute on Sunday, Aug. 12, 2012. (Associated Press)