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ABC News' Michael Falcone, Emily Friedman and Matthew Jaffe report:

Florida Sen. Marco Rubio officially threw his support behind Republican presidential candidate Mitt Romney Wednesday night in an appearance on Fox News' "Hannity" show.

"It's evidently and increasingly clear that Mitt Romney's going to be the Republican nominee," Rubio told Sean Hannity. "I am going to endorse Mitt Romney."

"He offers such a stark contrast to the president's record," he added.

Rubio said that the primary needed to come to a close and that Republicans must avoid a "floor fight" in Tampa this summer: "I don't think there's anything good about that."

"I think it's a recipe for disaster."

"I think all the candidates in this race have a lot to be proud of," speaking of the other Republicans running for the party's nomination, but he called Obama a "disastrous president" and suggested the GOP should begin to focus on the general election.

Perhaps more than any other Republican, Rubio's name is tossed around as a potential vice presidential  candidate. Rubio shot down that speculation on "Hannity" saying, "I don't believe I'm going to be asked to be the vice presidential nominee. "

He said as much in an interview earlier on Wednesday.

"It's not going to happen," Rubio told MSNBC's Andrea Mitchell. "But I'm obviously flattered by, that people think about me that way. There are some things I'd like to get done here in the United States Senate. I'm enjoying the role that we have here."

Mitchell noted that he would "have a lot more power as vice president, potentially."

"Oh, you think so?" Rubio replied, grinning widely. "I don't know. I mean that's debatable. Well, I'm enjoying my time here in the Senate. It's a privilege to serve here, and that's really what I'm focused on. I'm not going to be the vice presidential nominee, but I'm always flattered when people bring it up. I think they mean it as a compliment."

Tuesday, in an appearance on the "Tonight Show with Jay Leno," Romney was asked to describe Rubio in one word. Using three, Romney responded "The American Dream."

And in Metairie, Louisiana, on Friday, Romney referred to Rubio when making his argument against "Obamacare," saying that the Florida senator made a good point about the costliness of the plan:

"There's another one that Marco Rubio mentioned-the Senator from Florida-he said even if Obama care were a perfect piece of legislation-and it's not-we can't afford a trillion dollars of new spending," Romney said. "And we just heard from the CBO, it's not a trillion dollars, it's double that. And so, the critics were right, and the advocates were wrong. Obama care is massively more expensive than originally estimated and we cannot afford more government spending."

Rubio is taking other steps to shed his previously low-profile. The South Carolina GOP announced earlier this month that the Florida senator will be keynoting the party's annual Silver Elephant dinner on May 19.

And the publisher of Rubio's forthcoming memoir, "An American Son," announced that it was pushing up the release date from October to June 19.

 According to a late January poll conducted by Latino Decisions for ABC News and Univision, 60 percent of Latino Republicans in Florida would be much more likely to vote Republican in November if Rubio is added to the GOP ticket. Nationwide, 13 percent of Latinos said they would be much more likely to vote Republican if that happened, with 12 percent saying they would be somewhat more likely to back the GOP if Rubio joined forces with Romney.

That same poll found that 67 percent of Latinos would back Obama in a matchup against Romney, who only earned 25 percent of their support. 41 percent of Latinos nationwide said they had a somewhat unfavorable or very unfavorable view of Romney. And a whopping 72 percent of Latinos said the Republican candidates in the primary either didn't care too much about Latinos or were being outright hostile towards Latinos.

Rubio would obviously help Romney's cause in that regard.

The Florida senator has criticized his party's approach to Latinos. In February, Rubio told Time Magazine, "What's the Republican legal-immigration plan? And that's a problem, when all they [Latinos] hear from you is what you're against and not what you're for… Ultimately there is, in my opinion, hundreds of thousands of conservatives and potential conservatives all across this country that will never become conservatives because they somehow feel that the party where the conservative movement is housed doesn't want them."

While Romney consistently says it would be "presumptuous" to give names of people he'd consider for the vice president before he's the GOP nominee, often waving off the question by saying that the republicans have a "deep bench" that could fill the slot, that Rubio is on Romney's mind is undeniable.

Romney has not shied away from speaking highly of Rubio on the campaign trail, even coming to his defense last October when several publications challenged the year that Rubio's parents fled Cuba, arguing that the Florida senator may have embellished his family's history.

At a press conference at his Manchester, N.H., campaign headquarters, Romney was asked about the controversy, to which he leapt to Rubio's defense.

"I have the highest respect for Marco Rubio I think his family's history having come to this country speaks for itself. This is a family who came with nothing and Marco Rubio and his family deserve the highest praise and recognition. I think the world of Marco Rubio and support him entirely and think the effort to try to smear him was unfortunate and bogus," said Romney.

On Wednesday night, Rubio returned the favor: "We have an obligation to work on behalf of the nominee, Mitt Romney," he said.

"I have zero doubt in my mind of two things," Rubio said. "Number one, that Mitt Romney will govern as a conservative. Number two, he will be head and shoulders better than the guy who is in the White House right now."