Sen. Marco Rubio, R-Fla., endorsed Mitt Romney for president Wednesday night on Fox News' "Hannity," saying Romney offers "a very clear alternative" to President Obama's vision for the future of the country.

Rubio, a young, first-termer who has been discussed as a possible vice presidential candidate, criticized talk of a fight for the Republican nomination on the convention floor, a possibility that is keeping alive the campaigns of Rick Santorum and Newt Gingrich.

"I think that's a recipe for delivering four more years of Barack Obama," Rubio told Fox News' Sean Hannity.

Romney has "earned this nomination," Rubio said, though he again shot down questions about whether he would accept any offers of a spot on the ticket.

"I don't believe I'm going to be asked to be the vice presidential nominee," he said, adding it's not something he wants.

The endorsement comes after another big-name in Florida politics, former Gov. Jeb Bush, threw his support behind Romney, and former President George H.W. Bush is expected to officially endorse Romney on Thursday.

Romney has a comfortable lead in the delegate count, though Santorum has been able to pick up wins in several recent state contests, including Louisiana on Saturday.