Rubio stumps with Romney in Pennsylvania Florida Sen. Marco Rubio speaks in Miami Jan. 27, 2012.. ASTON, Pa., April 23 (UPI) -- U.S. Sen. Mark Rubio, R-Fla., joins likely Republican presidential nominee Mitt Romney on the campaign trail a day before primaries in five states. Rubio has been mentioned as a possible vice presidential candidate, although the freshman senator has expressed interest in representing Florida in Congress and sought to deflect some of the speculation about his future during the weekend, CNN reported. Rubio suggested former Florida Gov. Jeb Bush as a possible GOP vice presidential candidate, telling CNN Sunday Bush would make a "fantastic vice president." Romney has said he doesn't have anyone in mind as a running mate. Rubio was to join Romney in an event in Aston, Pa., Monday, Romney's Web site indicated. Tuesday's primaries in Pennsylvania New York, Connecticut, Delaware and Rhode Island are the first contests Romney will participate in without a major challenger. Former U.S. Sen. Rick Santorum of Pennsylvania, who had been the leading challenger, withdrew from the GOP field April 10. CNN said Romney, the former Massachusetts governor, will watch the results from New Hampshire, where he won his first primary in his White House bid.