DES MOINES — The attacks began three weeks ago and have not let up since: Television ad after television ad slamming Newt Gingrich for having “more baggage than the airlines,” for being fined by Congress for ethics violations, for his position on illegal immigration, even for admitting that he has made mistakes on the campaign trail.

Super PAC 'Restore Our Future' has spent close to $3 million in Iowa alone. Democrats and Republicans alike have singled out the $2.8 million-and-counting air deluge as the biggest factor in Mr. Gingrich’s precipitous drop in polls of Iowa voters and Mitt Romney’s corresponding rise, reshaping the critical first contest of the Republican primary season to Mr. Romney’s benefit.

The ads, which continue to blanket Iowa days before the caucuses here, were created and paid for by people with deep knowledge of the Romney campaign’s strategic thinking, close relationships with Mr. Romney’s most generous donors, and even research on what television viewers like and dislike most about Mr. Romney himself.

Yet neither Mr. Romney nor his staff has had to lift a finger or spend a dollar to make it happen. In a stark illustration of how last year’s landmark Supreme Court ruling on campaign finance has created powerful new channels for outside money to influence elections, the negative onslaught is the work of a group called Restore Our Future.

The most prominent of the “super PACs,” which can accept unlimited donations for purposes of supporting or attacking candidates, it operates independently of the Romney campaign but under the direction of former Romney aides who do not need to be told what the candidate needs.

They include Carl Forti, the political director of Mr. Romney’s 2008 campaign; Charles R. Spies, Mr. Romney’s former chief counsel; and Larry McCarthy, an alumnus of Mr. Romney’s media team who was known for producing some of the more compelling positive spots for Mr. Romney four years ago, but has nonetheless earned a reputation as one of the most fearsome political ad makers in the country — he produced the Willie Horton commercial that devastated Michael S. Dukakis’s presidential campaign in 1988.

Restore Our Future’s fund-raiser, Steve Roche, led the Romney campaign’s own finance team until this summer. He now spends his days meeting with the New York hedge fund managers, Utah businessmen and Boston financiers who have contributed almost $30 million to the group this year, according to people with knowledge of the group’s fund-raising. Among the donors are some conservatives who have a long history of backing attack-oriented outside groups like Swift Boat Veterans for Truth, which in 2004 went aggressively after Senator John Kerry, the Democratic presidential nominee that year.

The result: Mr. Romney has effectively outsourced his negative advertising to a group that has raised millions of dollars from his donors to inundate his opponents with attacks — all without breaking the rules that forbid super PACs to explicitly coordinate with candidates. Polls showed Mr. Gingrich’s support in Iowa tumbling immediately after the Restore Our Future ads began running in early December. An NBC News/Marist poll released Friday showed a 19 percentage point increase over the last month, to 35 percent, in the number of likely Republican caucusgoers who said they judged Mr. Gingrich to be unacceptable as the party’s nominee.

“Restore Our Future has been very important,” said Mel Sembler, a top Republican donor and a member of Mr. Romney’s Florida finance team. “They’ve had an impact, there’s no question about it.”

The battle in Iowa has underscored what advocates for tighter campaign finance restraints have warned for months: that the new groups will be deployed to devastating effect, in the primary season and then in the general election.

“Iowa is ground zero of what we can expect in every competitive state for the rest of the presidential election,” said Ellen S. Miller, executive director of the Sunlight Foundation, which tracks outside money in politics.

“Iowa is ground zero of what we can expect in every competitive state for the rest of the presidential election,” said Ellen S. Miller, executive director of the Sunlight Foundation, which tracks outside money in politics.

Since they began advertising in earnest several weeks ago, groups like Restore Our Future have spent millions of dollars in the early primary states, rivaling and in some cases surpassing the spending of the candidates they support. While the candidates can raise just $2,500 from each individual donor for the primary, super PACs, thanks to the Supreme Court’s Citizens United decision, face no such restrictions.

Speaking on Fox News last week, Mr. Romney played down the significance of Restore Our Future’s advertisements against Mr. Gingrich, arguing that Mr. Gingrich was falling in polls as voters focused on his record. Mr. Gingrich has also been under intense assault from other groups, including Ron Paul’s campaign; Mr. Romney’s campaign itself called attention to Mr. Gingrich’s tumultuous departure from Congress in a mailing it sent to Iowa voters.

But one thing is clear: Restore Our Future has spent more on advertisements in Iowa and elsewhere than any other super PAC, according to tracking by NBC and Smart Media Group Delta. The group has already begun buying television time in two other Republican primary states, Florida and South Carolina, running ads that hammer Mr. Gingrich and Gov. Rick Perry of Texas.

A super PAC supporting Mr. Gingrich, Winning Our Future, has spent just $263,000 on advertising in Iowa, according to figures from NBC and Smart Media Group Delta, without explicitly attacking Mr. Romney. (Another pro-Gingrich group, Strong America Now, has attacked Mr. Romney in mailings to voters.) Restore Our Future has spent twice as much money in the state as Mr. Romney has, most of it on advertisements savaging his opponents. Meanwhile, Mr. Romney’s campaign has run only positive television ads, featuring sunny portrayals of him and his family, with the occasional jab at President Obama.

That has helped Mr. Romney avoid the classic conundrum of political attack advertising in a nominating battle: Negative commercials tend to harm both the candidate making the claim and the one on the receiving end. One aide said Mr. Romney has apparently suffered “no collateral” damage from Restore Our Future’s negative advertisements against Mr. Gingrich, which are not identifiably connected to Mr. Romney.

In recent days, Mr. Romney has tried to distance himself from the group. “We really ought to let campaigns raise the money they need and just get rid of these super PACs,” Mr. Romney said on MSNBC.

But in July, Mr. Romney appeared before dozens of potential donors to Restore Our Future at an organizational meeting, effectively blessing its work.

Should Mr. Romney win his party’s nomination, the group is poised to play as pivotal a role in a general election matchup against Mr. Obama, whose aides are keeping a close watch on it. (Former Obama aides have also formed a super PAC, Priorities USA Action.)

Restore Our Future will not be required to disclose its most recent donors until the end of January. But in disclosures filed this summer, the group reported $12 million in contributions, much of it from friends and past business associates of Mr. Romney.

Edward Conard, who gave a million dollars to Restore Our Future, is a former top executive at Bain Capital, the private equity firm Mr. Romney helped start. Another donor is J. W. Marriott Jr., chairman of the hotel chain, on whose board Mr. Romney served on until January. The group has also raised money from Sam Fox and Bob Perry, conservative businessmen who helped finance Swift Boat Veterans for Truth.

The group’s backers appeared to be briefly spooked when word circulated that Sheldon Adelson, a wealthy casino magnate who is close to Mr. Gingrich, had committed $20 million to a super PAC supporting him. One of Restore Our Future’s donors called Mr. Sembler in a panic, he said, and asked him to call Mr. Adelson — the two men are friends — to find out if it was true.

“I did call Sheldon,” Mr. Sembler said. “And he said, ‘I’m not only not giving $20 million, I haven’t given any money at all.’ ”