COLUMBIA, S.C. (AP) - With independent groups known as super PACs playing a pivotal role in the presidential contest, the Republican hopefuls are increasingly calling one another to account for the ads run by groups backing their candidacies.
The pressure on front-runner Mitt Romney, who has benefitted mightily from a blizzard of super PAC-funded attack ads against his rivals, has been especially strong.
No one has played the game more shrewdly than the former Massachusetts governor, who has risen to the top of the GOP field thanks in large part to the ads run by Restore Our Future, a super PAC staffed by his longtime advisers. The ads depict both Newt Gingrich and Rick Santorum as unscrupulous Washington insiders, to devastating effect.
In a nationally televised debate this week from South Carolina, Romney called super PACs "outrageous" and said he'd prefer that they weren't a factor in the race.
"Let people make contributions they want to make to campaigns. Let campaigns then take responsibility for their own words and not have this strange situation where we have people out there who support us, who run ads we don't like," Romney said in the debate.
In fact, Restore Our Future has been a bulwark of Romney's campaign, taking on the task of doing all the negative advertising on his behalf. That saves his campaign millions in television costs while allowing the candidate himself to keep his distance from unsavory attacks on his rivals.
Super PACs can raise unlimited amounts but are barred by law from coordinating with the candidates they support, and Romney professes to have no influence on the group's strategy and spending. His opponents, desperate to slow Romney's momentum before South Carolina's primary Saturday, call that a disingenuous dodge and are pressing him to disavow the ads.
"Gov. Romney's super PAC, over which he apparently has no influence ... makes you wonder how much influence he'd have if he were president," Gingrich said to applause in Monday's debate.
The new PACs, born of a 2010 Supreme Court decision easing campaign finance restrictions, are facing the first major test of their influence in presidential politics.
An Associated Press analysis this week found that ad spending by super PACs has been the most influential factor in the primary contests so far, more important than personal candidate speeches and other appearances.
So when the candidates profess frustration with the groups, it can sound like they protest too much.
"The candidates are using the law as cover to duck responsibility and duck accountability," said John Geer, a Vanderbilt University political science professor who studies campaign ads.
Geer pointed out that third-party campaign ads aren't new; the "swiftboat" ads run by allies of President George W. Bush helped sink John Kerry's candidacy in 2004. "What's new is the amount of money being spent on them," Geer said.
Restore Our Future pummeled Gingrich with some $3 million in negative ads in Iowa, reducing the former House speaker from a top-tier contender to fourth-place finisher in Iowa and in New Hampshire a week later.
The group has spent at least $2 million pounding both Gingrich and Santorum in South Carolina as the two battle to become Romney's chief conservative rival before the state's first-in-the-South primary.
Gingrich cried foul over Restore Our Future's ads in Iowa, accusing Romney of "buying millions in attack ads through a phony super PAC run by his former staff, paid for by his millionaire friends." He called on Romney to be "man enough" to take responsibility for the content of the ads.
Now, anger over super PACs is boiling over in South Carolina.
In Charleston on Tuesday, Rick Santorum blasted Romney for an ad by his super PAC suggesting that Santorum supports voting rights for felons. The former Pennsylvania senator voted for a bill that included a provision allowing prisoners to vote once they had completed their sentences and parole.
Romney is "playing dirty, dishonest politics" by refusing to accept responsibility for the ads, Santorum said. "The lie they are putting out there is a lie that he is going to stand behind," he added.
But Santorum himself arguably owes the survival of his campaign to a similar group, the Red White and Blue Fund, which is funded in part by Wyoming billionaire Foster Friess. The super PAC has helped Santorum's cash-strapped candidacy by spending more than $1.3 million on ads in early voting states, including South Carolina.
Romney stood by the Restore Our Future ad's message at a campaign appearance Tuesday while insisting again that he had no control of the ads Restore Our Future is running.
"I hear that Rick Santorum is very animated that the super PAC ad says he is very in favor of felons voting," Romney said. "Well, he is. That's his position."
Santorum had initially confronted Romney on the ad at Monday's debate, after Romney claimed anew that super PACs are "completely out of the control of candidates."
Santorum shot back, "If I had something - the super PAC that was supporting me - that was inaccurate, I would go out and say, 'Stop it.'"
Santorum's complaints apparently had an effect - Restore Our Future omitted a mention of Santorum supporting felon voting rights in a new ad released Wednesday in South Carolina.
For his part, Romney has criticized Gingrich for a film produced by Winning Our Future, a super PAC backing the former House speaker.
The film, "King of Bain," paints Romney as a corporate raider who fired people and bankrupted companies while he led the private equity firm Bain Capital, but it's full of inaccuracies.
"It's probably the biggest hoax since Bigfoot," Romney said in the debate.
Gingrich himself has backed away from the film, calling on the super PAC to edit it or take it down. But the film echoes a core Gingrich campaign message - that Romney's history at Bain will make him a ripe target for Democrats if he wins the Republican nomination.