In the Senate, Rubio has several characteristics that set him apart from most of his Republican colleagues.

Unlike most of his colleagues, Rubio is not a wealthy man. He did not grow up with money and soon after he was elected to the Florida legislature he had to give up his car and move into his mother-in-law's house. He still owed significant debt on his student loans when he was elected to the Senate, although thanks to the royalties from his book, he has now paid them off.

Not exactly an NFL prospect

After high school, Rubio earned a football scholarship to a college in Missouri, playing cornerback. He soon transferred back to Florida as the school ran into financial difficulties, and he admits he was never destined to be NFL material. Instead, he jokes about how ironic it is that his wife made it to the NFL but he didn't come close.

Still, when former Miami Dolphins quarterback Dan Marino threw him a few passes on the floor of the Florida House in 2006, with a crowd watching, Rubio showed his stuff -- first making an easy catch, but then also some harder ones.

He is younger than all the other senators, except Mike Lee of Utah, who is a week younger, so he may be mistaken for a junior aide in Capitol elevators.

But he also may have a better sense of younger generations than most of his colleagues. For example, in a recent interview posted on BuzzFeed, the senator offered a detailed discourse on rap and hip-hop. At the risk of offending some of his audience, he compared two top rappers from the 1990s by declaring, "Tupac's lyrics were more insightful -- apologies to Biggie fans." Asked by GQ to name his favorite rap songs, he listed "Straight Outta Compton" by N.W.A., "Killuminati" by Tupac, and Eminem's "Lose Yourself."

But when it comes to religion, he describes himself as a traditional Catholic -- albeit one who also was baptized Mormon when his family converted for a few years while living in Las Vegas. More recently, he has supplemented Catholic Masses by also attending services at a Baptist church in Miami, according to his office.

As soon as he won his Senate race, Rubio drew speculation about potential presidential aspirations and immediate comparisons to Barack Obama.

Like Barack Obama, Marco Rubio is young and well-spoken, comes from an ethnic minority and has only a few years of experience in the Senate. In addition, he came to Washington after serving in his state legislature, as did Obama, and he benefited greatly from a high-profile speaking role at his party's convention in 2012 -- as Obama did in 2004.

But Rubio has not been shy about his critique of the president, especially while he was campaigning for Romney last year.

"He is a bad president," Rubio said bluntly in his speech at the Republican National Convention in Florida last summer. "Under Barack Obama, the only change is that hope is hard to find."

Observers expect no less from his speech on Tuesday night.

Supporters in his hometown of West Miami will be watching closely. Rebeca Sosa is organizing a Rubio watching party at the same rec center where he first saw his future wife.

A few blocks away on the main drag of West Miami, an older man is holding a sign in front of Versailles Restaurant as the cars pass by on Eighth Street.

"Marco Rubio for president 2016," it says.