Sen. Marco Rubio, R-Fla., center (Credit: AP Photo/J. Scott Applewhite)
(CNN) -- With Mitt Romney now the presumptive Republican presidential nominee, the chatter has increasingly turned to the man or woman the former Massachusetts governor will tap to run alongside him during the general election.
Romney will campaign Monday in Pennsylvania with another senator and possible vice presidential pick, Marco Rubio of Florida.
Rubio was elected in 2010 aided by a wave of tea party support and a platform of fiscal conservatism. Speculation about his future has followed the freshman representative since then, something the impending release of his memoir has done little to temper.
Rubio, the son of Cuban immigrants, has become one of Romney's most ardent backers of late, but sought to deflect some of the attention over the weekend.
Rubio offered up former Florida Gov. Jeb Bush as a possible No. 2 on the GOP ticket, telling CNN Chief Political Correspondent Candy Crowley on CNN's "State of the Union" Sunday that he would make a "fantastic vice president."
Bush appeared to open the door to the position in an interview last week, but later told Bloomberg, "I am not going to be the veep nominee. Lay that to rest. I guess I wasn't clear enough."
Rubio is the latest in a series of supporters to appear under the VP spotlight around an event or series of events with Romney.
Joint appearances with Rep. Paul Ryan of Wisconsin, Gov. Nikki Haley of South Carolina, Gov. Chris Christie of New Jersey and Sen. Kelly Ayotte of New Hampshire and others have sparked similar chatter.
But the focus on Rubio has always been sharper, given his youth, popularity among many that associate with the tea party movement, battleground state roots and his place in the Hispanic community --- a crucial voting bloc in which Romney trails President Barack Obama badly in most polls.
The Pennsylvania appearances come a day ahead of the first primaries -- Pennsylvania, New York, Connecticut, Delaware, and Rhode Island -- Romney will take part in without a major challenger.
Rick Santorum, a former U.S. Senator from Pennsylvania, withdrew from the GOP field ahead of his home state's vote, as fund-raising slowed, the math appeared stacked against him, and his young daughter was hospitalized for the second time since he began campaigning.
The former Massachusetts governor will watch the results from New Hampshire, where he scored the first political victory of his campaign for the White House.
A campaign aide told CNN that the Granite State is "where the campaign kicked off, and we see this Tuesday as when the general will kick off -- so are going back to where it all started."