By Alina Selyukh
WASHINGTON (Reuters) - The U.S. presidential election is nearly 10 months away, but the theme of the 2012 campaign already seems set: It's the Year of the PAC Attacks.
Political action committees (PACs) - groups with great clout in U.S. politics that are legally separate from candidates - have spent more than $25 million this campaign season, with much more to come. Nearly half of that amount has bought messages, typically TV and radio advertisements, criticizing candidates.
A 2010 U.S. Supreme Court ruling that the government cannot restrict political speech and spending by corporations, unions and other outside groups allowed PACs to raise and spend unlimited amounts of money in campaigns - creating what are known as Super PACs.
Various PACs now are pouring money into an advertising war in South Carolina, whose primary Saturday is the next contest in the state-by-state battle for the Republican presidential nomination to face President Barack Obama, a Democrat, in the November 6 U.S. election.
The primary is seen as a crucial test of whether any of the other Republican candidates can slow frontrunner Mitt Romney's march toward the party's nomination.
PACs generally support a particular candidate or political cause. Although separate from the campaign they support, PACs typically are intimately familiar with a candidate's strategy.
And this campaign season, the PACs have taken over from candidate's official campaigns much of the dirty work of running negative ads aimed at hurting rivals.
In South Carolina, PACs backing individual candidates already have spent $4.6 million in "negative" ads attacking other candidates, according to a Reuters analysis of Federal Election Commission (FEC) filings.
Another $1.7 million has been spent in the state on "positive" ads promoting a candidate, the Reuters analysis indicates.
The actual spending numbers for both categories are likely higher because it can take a few days for expenditures to show up in FEC reports.
Voters in South Carolina, like those earlier this month in the Iowa and New Hampshire contests that opened the nomination race, have been bombarded by radio, TV and Internet ads.
Most of what they are seeing is negative advertising.
There are controversial advertisements placed by Winning Our Future, a PAC supporting former House of Representatives speaker Newt Gingrich, that blast Romney's record as a private equity executive, calling him a corporate raider and a job killer who laid off thousands of workers.
And there are ads by Restore Our Future, the pro-Romney group that helped to drive down Gingrich's poll numbers a month ago with a wave of ads accusing him of being a Washington insider with questionable ethics.
The group is continuing those attacks in South Carolina and has found a new target: former Pennsylvania U.S. senator Rick Santorum, who has become more of a threat to Romney after doing well in the Iowa caucuses and being endorsed by a group of influential evangelical Christian ministers.
A Restore Our Future ad accuses Santorum of voting for unnecessary spending while in the Senate and blasts him for voting to allow convicted felons to vote after they complete their sentences.
THE DENIABILITY DEFENSE
During Monday night's debate for Republican candidates in Myrtle Beach, Santorum went after Romney, saying the ad by Restore Our Future was misleading.
Romney responded with what has become the deniability defense for candidates in the age of Super PACs: that the ad criticizing Santorum didn't come from Romney's campaign, so Romney had no control over it.
"If they ever run an ad that's not accurate, I hope they take out the ad and make it correct," Romney, a former Massachusetts governor, said of the PAC that supports him.
"I did not have a Super PAC run an ad against you," Romney told a visibly irritated Santorum, adding that "there've been some attacks against me that have been outrageous and completely inaccurate."
The ad wars are particularly intense in South Carolina because the stakes in Saturday's primary are the highest they have been in the Republican campaign.
Conservatives Gingrich, Santorum and Texas Governor Rick Perry are desperate to prevent Romney from locking up the nomination. Romney won the initial contests in Iowa and New Hampshire, and leads polls in South Carolina and Florida, which holds its primary on January 31.
The winner of South Carolina's Republican presidential primary has gone on to win the party's nomination in every election since 1980. Many analysts believe Romney's path to the nomination would be nearly clear if he can win Saturday.
Like his campaign, the PAC supporting Romney has far outdistanced its rivals in spending. Restore our Future has reported spending $8.1 million during the overall campaign.
Much of that money has gone toward attack ads against Gingrich, who during the campaign has been the subject of $7.8 million in attack-ad spending by the pro-Romney PAC and other groups, according to a Reuters analysis of FEC reports.
Gingrich, by far, is the most attacked Republican candidate in campaign ads. Romney is next, having been the subject of negative ads costing $3.2 million.
The spending against Romney is likely to soar by the end of this week.
Winning Our Future, the pro-Gingrich PAC, has vowed to spend $3.4 million in South Carolina alone. To date, it has spent just $3.7 million in the entire campaign and is investing heavily in anti-Romney spots.
South Carolina is where Romney is getting his first real taste of the type of negative ads he could face this fall as the Republican nominee opposing Obama's well-funded campaign.
"Romney has gone almost until now without any negative ads running against him," said Bill Burton, who runs the pro-Obama PAC called Priorities USA Action.
Burton's group has run ads attacking Romney but has stopped advertising in South Carolina, preferring to let the Republicans battle it out among themselves.
'IT'S A CAGE FIGHT'
"This is a time when everyone picks up a knife and throws it. ... It's a cage fight when you come to South Carolina," said Barry Wynn, an influential Republican donor in the state.
Last week, Wynn backed away from supporting Perry to stand behind Romney after Perry joined Gingrich in blasting Romney's conduct as CEO of Bain Capital LLC, the private equity firm.
Restore Our Future, the pro-Romney group, says it has spent about $2.5 million in South Carolina. Some of its ads have promoted Romney, but most have targeted Gingrich and Santorum.
Make Us Great Again, the pro-Perry PAC, is second only to the pro-Romney group in overall spending. The group has spent $4 million in the campaign overall.
It launched an ad last Friday that sought to differentiate Perry from Gingrich and Santorum, with whom the Texas governor is competing for support among the evangelical Christians who make up about 60 percent of South Carolina's Republican voters.
Make Us Greate Again says it plans to spend $1.9 million in South Carolina, which could be Perry's last chance to make a move in the nomination battle.
The pro-Santorum Red White and Blue Fund has spent $800,000 on ads in South Carolina but has refrained from negative advertising in the state.
So have the Super PACs supporting U.S. congressman Ron Paul of Texas and former Utah governor Jon Huntsman, who on Monday suspended his campaign, endorsed Romney and called on the remaining candidates to tone down the negative ads.
Some South Carolinians say they are so annoyed by the deluge of negative ads that they may skip the primary.
"The volume of negativity has never been quite so great," Wynn said. "We (in South Carolina) kind of enjoy this kind of stuff -- we're a strange lot out here -- but even we get tired."
The volume of attacks ads in the campaign is mocked in a new ad by late-night TV comedy show host Stephen Colbert, who has formed his own Super PAC that has so far reported spending $21,600 on attacking Romney.
In the ad, Colbert takes Gingrich's criticisms of Romney as a job killer to an absurd level, reasoning that because Romney's firm laid off workers from several companies it took over, Romney must be a "serial (job) killer."
Representatives of Super PACs hesitate to comment on voters' concerns about negative ads.
Asked whether such backlash is a consideration when the pro-Perry group weighs how many ad placements to buy in a state, spokesman Jason Miller said, "People buy ads because they work."
(Additional reporting by Alexander Cohen; Editing by David Lindsey and Will Dunham)