John McCain tells Romney: 'I chose Sarah Palin as I trusted her'

One of the names mentioned as a possible Romney running mate is Cuban-American Marco Rubio, a 40 year-old senator from Florida who is a favourite of "Tea Party" conservatives.

Rubio, speaking on "Fox News Sunday," said the economy was worse off under Obama, and dismissed the president as a divisive Washington politician.

"All of the things that made him different and special four years ago are gone, and now, all he does is run dividing Americans against each other, obviously, because he can't run on his record," said Rubio.

But he dodged questions about a possible vice presidential run with Romney.

"I'm not going to talk about the vice presidential process," Rubio said. "But I can tell you that there are multiple ways that someone can help our nominee and I look forward to doing that."

Vice President Joe Biden joked that he might be interested in running in 2016 paired on a ticket with Secretary of State Hillary Clinton.

"I think we may run as a team," Biden told NBC's "Meet The Press" when asked to discuss his political future.

"I'm only joking obviously," Biden quickly added. "I don't know. I don't know whether I'm going to run and Hillary doesn't know whether she's going to run."

It was unclear from Biden's remarks which of the two political heavyweights would head the putative ticket.

Mrs Clinton, who ran a tight campaign against Obama in 2008 in a failed bid to win the Democratic nomination, has at least publicly ruled out any further White House bids.

But Biden said he was certain that he will be Obama's 2012 running mate, despite speculation the president would try to strengthen the ticket's appeal by choosing Mrs Clinton instead.

"There is no question about it. There's no way out. They've already printed Obama-Biden (campaign posters)" he said. "You are looking at the vice presidential candidate of the United States of America."

Source: agencies