A campaign group supporting Mitt Romney for the 2012 Republican presidential nomination spent almost $10m in February on ads and other material attacking his main rival Rick Santorum and only $52,000 on positive spots.
The figures underline how super-political action committees and their negative attacks are dominating the Republican race, and contain a preview of the outsized role they are likely to play in elections in November.
The February campaign spending figures for the pro-Romney super-Pac Restore Our Future and other campaigns were released on Tuesday by the Federal Election Commission.
Scores of super-Pacs, many of which now have multimillion-dollar war chests, were set up in the wake of two 2010 court decisions lifting all limits on corporate, individual and union donations to political campaigns.
The super-Pacs are not allowed to co-ordinate with candidates, although in practice their spending has run in tandem with their favoured politicians’ campaigns.
In February, at a time when Mr Santorum emerged as Mr Romney’s chief rival ahead of Newt Gingrich, Restore Our Future trained its guns on the former Pennsylvania senator in campaigns in Michigan, Arizona and other states.
Restore Our Future said it spent $9.95m on anti-Santorum material, such as TV and radio ads, and direct mail, $1.6m against Mr Gingrich and only $52,000 on spots favouring Mr Romney.
Mr Romney has continued to hammer his rivals ahead of Tuesday’s Illinois primary, outspending Mr Santorum by nine to one, according to some estimates.
Mr Romney’s own campaign raised $12m but spent $12.3m, leaving it with $7.7m in the bank.
The website, OpenSecrets.org, calculates that the 385 super-Pacs registered with the FEC have so far reported raising $131m since the 2010 elections and have spent $79m.
The super-Pacs have transformed the Republican primaries, by giving candidates whose formal campaigns have raised little money the firepower to stay in the race, even if they are accumulating few delegates.
Many Republicans are increasingly concerned about the drawn-out race, believing it is damaging their chances against President Barack Obama in November, but there is little they can do.
“The only way they can stop the candidates is to put their donors’ heads in a vice, and say stop giving money, but they can’t do that,” said Norm Ornstein, of the American Enterprise Institute.
On Tuesday, Mr Santorum’s campaign announced it raised $9m in February, more than double what he raised in January. The campaign said his battle with Mr Romney had helped to bring in donations.
Bob Perry, the Texas home builder, was the largest single donor to Restore Our Future in February, giving $3m. He has given $4m to the fund since the beginning of 2011.
Other donors to the pro-Romney group include financiers Ken Griffin of Citadel, the hedge fund, and Henry Kravis, the private equity executive, who both gave $100,000.
Harold Simmons, a Texas businessman, who has given more than $16m to super-Pacs and campaign since 2010, also gave $100,000 to Restore Our Future.
Mr Gingrich’s super-Pac, which has raised far more money than his formal campaign, received $5m from its biggest donors, Las Vegas casino magnate Sheldon Adelson and his wife, who gave $2.5m each in February. The pair have already given $10m to the pro-Gingrich super-Pac Winning Our Future.
Leslie Moonves, of CBS, the broadcaster, said in late February the super-Pacs have been spending so much money on ads that they “have sort of changed the amount of money in the marketplace” to the benefit of broadcasters.
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