Sen. John McCain (R-Ariz.) said that the unrestrained spending on attack ads by super-PACs is having a “damaging effect” on the Republican field of candidates, and worried that it might be a “real danger” to the eventual nominee in the general election.

McCain, who last week endorsed GOP front-runner Mitt Romney, made the comments Monday on CNN.

“I think it’s a real danger, and obviously I’d like to see it over with a Romney win in South Carolina followed by one in Florida,” he said. “I think there will be plenty of time for our nominee to recover, but it certainly has a damaging effect.”

{mosads}Newt Gingrich was hammered in the polls following an onslaught of attack ads from political action committees that back his rivals. After pledging to run a positive campaign, the former House Speaker reversed course over the weekend.

“I spent three weeks saying, ‘Let’s find a way to be positive,’ ” Gingrich told reporters Monday. “Fine. I have broad shoulders. I can stand the heat. Now we’ll see if he has broad shoulders and can stand the heat.”

Gingrich has recently referred to Romney as a “liar,” and at Sunday’s New Hampshire debate told him to “drop the pious baloney.” 

McCain said Gingrich is going too far. 

“You’re not helping yourself much because I think you still have to give people a reason to vote for you, and I don’t think that some of the language he’s using is normal to be used in even the most heated of campaigns,” he said. 

“I’ve said several times that that’s not something that I think is language that most voters would respond to in a positive fashion,” McCain continued. “I think there was a sense that [Gingrich] had in his own words that it was inevitable that he was going to win the nomination, and apparently now it looks like he’s not, and I think it has stung him rather badly.”

Negative campaigning has been a sticky issue for the Republican candidates this year, as it’s the first presidential primary since the Supreme Court’s 2010 Citizens United decision to allow unlimited donations to super-PACs. 

McCain blamed the Supreme Court for the campaign season’s nasty turn.

“I think part of it is symptomatic of primaries, which are always tough, and sometimes even more personal in the attacks than the general elections are,” he said. “But it’s also the result of the worst decision, I think, in at least the last 50 years or so, of the United States Supreme Court called Citizens United, where they basically unleashed without transparency, without accountability, huge amounts of money from these so-called independent campaigns, which you and I know are not independent.” 

Gingrich at first called on Romney to disavow ads from his super-PAC, saying they were untrue. Romney responded that campaigns are not legally allowed to be in contact with the super-PACs, and Gingrich has since adopted that argument as well. 

A super-PAC that backs Gingrich will soon be releasing a 27-minute documentary skewering Romney for his time at Bain Capital.

McCain said that no matter what you think of it, going negative against an opponent has proven to be an effective campaign strategy. 

“We all decry it,” he said. “But as long as it moves numbers, money will be invested in that kind of campaigning, and I’m sorry to say it, but that happens to be a reality.”