01/05/2012 09:01 am ET

John McCain Endorsement: Arizona Senator Tells Republicans To Settle On Mitt Romney

WASHINGTON -- Just two days after the first votes in the race to pick a Republican presidential nominee, Sen. John McCain said it's time to wrap things up.

McCain, who endorsed Mitt Romney to be the GOP nominee a day earlier, said Republicans need to "get this thing done with as quickly as possible and get into the main event."

The Arizona senator, speaking Thursday on CBS' "The Early Show," says Republicans need to focus on beating President Barack Obama.

(Video above via CBS News.)

McCain and Romney were rivals for the GOP nomination in 2008. That time, it was McCain who came away with the nomination, only to lose the presidency to Obama.

McCain defended Romney's consistency on issues, which he attacked in 2008 as a GOP presidential candidate. "He's done a lot since then," said McCain. "All of us from time to time over the years change our positions as certain conditions and circumstances change, but I don't think there's anyone in america that has changed positions more times than the President of the United States on virtually every issue."

He also criticized Newt Gingrich for calling Romney a "liar" Tuesday for being disingenuous about negative ads run against him by a Romney-aligned super PAC. "I don't think it’s appropriate to call your opponent a liar. That's just something we don’t do in politics unless you certainly have some overwhelming proof," he said.

McCain went on to call the Citizens United decision that altered the campaign finance landscape "one of the worst decisions in history." He said, "But I predicted when the U.S. Supreme Court -- with their absolute ignorance of actually what happens in politics -- struck down that law that there would be a flood of money into campaigns. Not transparent; unaccounted for. And this is exactly what is happening." He added, "And those are the rules, and everyone is playing by those rules."