He's young, telegenic and charismatic. He's Hispanic, Catholic and the son of Cuban immigrants. He's a tea party favorite, a GOP star and, many say, the future of the Republican Party.
Sen. Marco Rubio's endorsement would be a big get for any of the presidential contenders ahead of the Jan. 31 Florida primary -- if only he were the giving kind.
The freshman senator, who has ties to GOP presidential front-runners Mitt Romney and Newt Gingrich, has pledged to stay neutral as Republicans pick a challenger to President Barack Obama. But Rubio's refusal to pick sides hasn't squelched intense speculation about whether Rubio might make a surprise endorsement -- and whether he'll end up as the vice presidential nominee.
Rubio publicly insists that he's not interested in either, recently telling Fox News Channel: "I've had a lot of people running with whom I've had relationships and that have been helpful to me, so I'm really not inclined to endorse in the primary."
Aides to Romney and Gingrich say neither candidate has asked Rubio for his endorsement out of respect for the senator's decision to stay out of the race. Even so, their backers are privately hoping Rubio changes his mind, given how wide open the race is only a week before Florida's Republicans weigh in on what has been a volatile nomination fight.
Rubio, 40, is one of Florida's most popular leaders, particularly among Republicans. A Quinnipiac University poll released Jan. 10 found that nearly 80 percent of Republicans and nearly half of independents approved of the job he is doing. Only a quarter of Democrats liked his job performance.
A native of Miami, the former state legislator was the youngest person and first Hispanic to become speaker of the Florida House in 2007. He vaulted onto the national stage in 2010 when he latched onto the fledging tea party movement to challenge then-Gov. Charlie Crist, a centrist and the GOP establishment's choice, in the Republican primary for an open Senate seat. Rubio's stock rose quickly, forcing Crist to flee the GOP and run as an independent. In the end, Rubio was the GOP nominee and he went on to win in the general election.
Rubio has connections to both front-runners.
He and Gingrich have known each other for years. The freshman senator brought a photo of the former House speaker to his Washington office. And Gingrich wrote the forward to Rubio's book, "100 Innovative Ideas for Florida's Future." Rubio wrote it before taking office as Florida House speaker. Gingrich has called the book "a work of genius."
Rubio's personal friend and political ally, fellow Cuban-American U.S. Rep. David Rivera, is backing Gingrich. Rubio's former Senate campaign chief Jose Mallea is running Gingrich's Florida campaign. Rubio and Gingrich both will address the Hispanic Leadership Network's conference in Miami on Friday.
Romney, for his part, endorsed Rubio over Crist in the 2010 GOP Senate primary, calling him "an American hero" and adding: "He represents what is good and so great about this land of ours."
Nearly half a dozen Rubio staffers worked for the former Massachusetts governor's 2008 presidential campaign, including the senator's chief of staff.
Both Romney and Gingrich have called Rubio an obvious choice for a vice-presidential short-list.
"He checks a lot of boxes. He comes from Florida, and he provides balance," said former Florida Sen. Mel Martinez, a Romney backer. "I can't conceive of anyone who in a list of five or six wouldn't have Rubio there."
Bill McCollum, co-chair of Gingrich's Florida campaign, said Rubio would be among Gingrich's top picks for vice president "if and when the time occurs."
It's not just that he's from Florida, a critical general-election swing state, that has Republicans speculating about his political future.
His potential appeal to Hispanic independents could be a huge draw for the eventual GOP nominee. Rubio is immensely popular among Cuban exiles, one the GOP's most reliable and influential voting blocs in this state. And his popularity with the tea party could help inject the ticket with a dose of excitement, and help ensure these activists turn out in November to support the nominee.
"He comes across as genuine and that's why people like him," said Jennifer Korn, executive director of the center-right Hispanic Leadership Network.
Indeed, Rubio, who teaches political science at Florida International University in his spare time, is a natural on the campaign trail, equally comfortable giving passionate speeches about his parents' sacrifices as he is discussing how to restructure Social Security. He also has a captivating life story that he holds up as an example of the American Dream.
Then there's Rubio's strong record as a conservative.
He gave a wildly lauded speech on behalf of a free market and compassionate conservatism last summer at the Ronald Reagan Library in California. He opposed Obama's nomination of Supreme Court Justice Sonia Sotomayor, a Puerto Rican-American and the first Hispanic to be named to the court. He recently blocked another Puerto Rican-American's nomination for ambassador to El Salvador. While conservatives generally applaud both moves, they're not likely to play well with central Florida's fast-growing Puerto Rican community, a major swing vote in the state.
Meanwhile, his support among Hispanics is hardly rock solid nationwide. Rubio got into a public spat with Univision over how the No. 1 Spanish-language network handled a story detailing a decades-old drug conviction of Rubio's brother-in-law. He was forced to backpedal last year when it was revealed that his parents did not flee Fidel Castro's communist government as he had claimed. They were economic immigrants who arrived in the U.S. several years before the Cuban Revolution -- though they quickly came to oppose Castro and identify with the exile community.
Rubio also opposes comprehensive immigration reform and supports Arizona's tough new law targeting illegal immigration, putting him in stark contrast with the vast majority of the country's Latino voters.
Even though he's not endorsing in the presidential race, Rubio is having at least some effect on it.
Mindful of angering Rubio, nearly all of the GOP candidates declined to participate in a proposed Univision presidential debate last year. This week, Gingrich, Romney and Santorum agreed to participate in a "Meet the Candidates" forum co-hosted by the network.