** FILE ** In this Feb. 22, 2012, photo Republican presidential candidate and former Massachusetts Gov. Mitt Romney, right, talks with fellow candidate, former Pennsylvania Sen. Rick Santorum, after a presidential debate in Arizona. On Monday night, May 7, 2012, Santorum endorsed Romney, saying "above all else" they agree that Obama must be defeated. (AP Photo/Jae C. Hong, File)

Photo by: Jae C. Hong

** FILE ** In this Feb. 22, 2012, photo Republican presidential candidate and former Massachusetts Gov. Mitt Romney, right, talks with fellow candidate, former Pennsylvania Sen. Rick Santorum, after a presidential debate in Arizona. On Monday night, May 7, 2012, Santorum endorsed Romney, saying "above all else" they agree that Obama must be defeated. (AP Photo/Jae C. Hong, File)