Mitt Romney secured the backing of one of the last big prizes of the endorsement sweepstakes late Wednesday: U.S. Sen. Marco Rubio.
Rubio, the widely popular freshman Republican from Miami, announced his decision on Fox News' Hannity show Wednesday night, becoming one of the last major GOP figures to get behind Romney.
The surprise endorsement has the potential to give a shot of credibility to Romney, who has failed to excite the deeper conservatives of the Republican base, and instantly added to speculation that Rubio would be his running mate. Rubio was quick to dismiss the idea.
"We've got to come together around who I think has earned this nomination, and that's Mitt Romney," Rubio said, expressing concern that the protracted GOP primary with Romney's rivals Rick Santorum and Newt Gingrich would hurt the party's chances of defeating President Barack Obama in November.
Santorum and Gingrich have conceded they cannot catch up to Romney's large delegate lead but are determined to block him from getting the required 1,144 delegates before the Republican National Convention.
"There is no way that anyone can convince me that having a floor fight at the convention in Tampa in August is a recipe for victory in November," Rubio said. "On the contrary, I think it's a recipe for disaster. I just don't think that's a wise route to go.
"We've had a very good primary," he continued. "I think all the candidates have a lot to be proud of, but I think it's increasingly clear that Mitt Romney is going to be the Republican nominee."
Rubio's endorsement comes late in the game — he said for months he did not plan to endorse — and closely follows that of his political mentor, former Florida Gov. Jeb Bush.
But it is still significant, given Rubio's rising national status and conservative bona fides. He has feet in both the establishment circles and the tea party.
And he is Hispanic. Romney has adopted some hard line positions on immigration — as did Rubio during his 2010 run for Senate against then-Gov. Charlie Crist, but he has tried to moderate his positions since entering the Senate.
The embrace has potential downsides. Rubio's followers may see it as politically calculating and acquiescing to establishment politics. It also may intensify scrutiny of his positions of immigration and other issues.
On Fox, Rubio touted Romney's "private sector" experience as a businessman and work as governor as Massachusetts, saying he offers a "very clear alternative" to Obama.
Romney, in a statement, alluded to Rubio's life story as the son of Cuban immigrants who worked blue collar jobs in the U.S.
"Marco Rubio is living proof that the American Dream is still very much alive," he said, deeming the endorsement a "major milestone" his campaign.
Fox host Sean Hannity asked about Romney's troubles with some conservatives, and Rubio said one upside to the primary is it has made candidates take "very strong positions on issues that we can hold them accountable to."
He said he has "zero doubt" that Romney would govern as a "conservative."
Rubio again discounted talk he would serve as Romney's running mate, saying his heart and mind are in serving Florida in the Senate: "I don't believe I'm going to be asked to be the vice presidential nominee. That's not what I intend to be, that's not what I want to be and that' not what's going to happen."
Ana Navarro, a Republican strategist from Miami and Rubio ally, said, "Romney still needs to reassure the conservative base, and support from Jeb, (Sen. Jim) DeMint and now Rubio sends a message to conservatives that the fat lady is warming up her vocal cords."
Rubio "is astute and it's smart to do this while it still matters," Navarro said. "It's no fun to show up at a party after it's over and the lights have been turned off.''
Romney is set to collect another high-profile endorsement today — former President George H.W. Bush.
Santorum continues to attack Romney on the campaign trail but has said he would be open to serving as his running mate if it comes to that.