Romney is increasingly turning his attention to President Barack Obama.

“This man is out of ideas, he is out of excuses, and in 2012 we are going to make sure he gets put out of office!,” Romney said.

Romney’s first major decision will be to select a vice presidential running mate, and one of those expected to be on his short list of candidates is Senator Marco Rubio of Florida.

Rubio says he would be flattered to be asked, but he says the answer is no.

“Because I’m enjoying my service in the Senate,” Rubio said. "I don’t want to be the vice president right now or maybe ever.”

Other possible contenders include Representative Paul Ryan of Wisconsin and New Jersey Governor Chris Christie. But Christie also says he is not interested.

“But he knows it is not my desire, my lifelong wish, to be vice president of the United States,” Christie said.

Romney’s choice is important, says former Reagan Chief of Staff Ken Duberstein.

“Whoever a presidential nominee selects as vice president, as his nominee, that is the first major judgment that the American people see about that presidential candidate,” Duberstein said.

Four years ago, Republican John McCain’s decision to pick Alaska Governor Sarah Palin hurt him with independent voters, something Romney is likely to try to avoid, says Duberstein.

“In light of 2008, Governor Romney, I think, will go with somebody who everybody will perceive can step in and be president in a heartbeat. If you are going to select somebody as one step away from the presidency, that person has to be prepared to be president on the very first day,” he said.

Historically, vice presidential running mates are not major factors in presidential elections.

But they can offer small advantages, says political analyst Rhodes Cook.

“It can be important more in terms of, say, a certain state. If there is someone who can help bring you a major state, be it Florida, Ohio, Michigan, something like that. Then yes, it could make a difference,” Cook said.

Romney is expected to secure the number of delegates he needs for the Republican nomination in June, but the search for a running mate is expected to take longer.