South Carolina voters are being buried this week under an avalanche of combative and often nasty political commercials from super PACs, funded by a tiny group of super-rich donors with very particular interests in the state’s Republican presidential primary.

Hedge-fund king John Paulson, who donated $1 million to a group backing former Massachusetts governor Mitt Romney, would very much like to see President Obama’s financial reforms repealed. The Marriott brothers, who also gave $1 million to a pro-Romney super PAC, have lobbied Washington for favorable tax and immigration policies through their hotel companies.

And casino magnate Sheldon Adelson recently dashed off a $5 million check to a group backing former House speaker Newt Gingrich (Ga.), marking what may be the largest single political contribution in U.S. history. Adelson is well known for supporting hard-line policies favoring Israel while also advocating measures that would benefit the gambling industry.

“There are probably fewer than 100 people who are fueling 90 percent of this outside money right now,” said David Donnelly, national campaigns director at the Public Campaign Action Fund, an advocacy group favoring limits on political spending. “When you think about the amazing impact that this small number of people have on deciding the election, on the information that people will have on who to vote for, it’s mind-boggling.”

The departure of former Utah governor Jon Huntsman Jr. from the field on Monday also underscores how few rules govern super PACs, which are free to shift their support and money to another candidate or cause once their main beneficiary bows out. A group called Our Destiny PAC spent $2.5 million backing Huntsman, bankrolled in part by his billionaire industrialist father; its future plans are unclear.

In total, these new and unrestrained political action committees spent more than $15 million supporting GOP candidates in Iowa and New Hampshire and are now outspending the official campaigns in South Carolina by 2 to 1, according to advertising and expenditure data.

The onslaught of outside money has already shaped the contours of the race, shoring up Romney in Iowa and giving candidates such as Gingrich (Ga.), former senator Rick Santorum (Pa.) and Texas Gov. Rick Perry a last chance to break through in South Carolina.

Sporting anodyne names such as Endorse Liberty and Make Us Great Again, super PACs are taking advantage of recent court rulings allowing corporations, unions and wealthy individuals to spend as much as they want on elections. The groups have quickly evolved into de facto shadow operations of the traditional campaigns, despite rules forbidding direct cooperation between the two.

Super PACs are generally staffed by former aides of the candidates they support, and they are fueled by benefactors wealthy enough to write six- and seven-figure checks for what amounts to a political gamble. The biggest super-PAC donors also are often fundraisers for the candidates: A Wall Street event for Romney on Tuesday includes at least six hosts who gave to the main pro-Romney super PAC as well.

Many of the donors will remain anonymous until Jan. 31, when reports to the Federal Election Commission are due. But previous disclosure records, combined with leaks and news reports, sketch out a varied list of tycoons, hedge-fund managers and industrialists behind many of the donations, with a pronounced tilt toward Wall Street and the powerful financial services industry.

Restore Our Future, the pro-Romney super PAC, spent $7.8 million on the primaries through last week thanks to contributors dominated by Wall Street and the real estate sector. Several donors — including Edward Conard, who gave $1 million, and Paul Edgerley, who gave $1 million together with his wife — have ties to Romney’s former equity fund, Bain Capital.

J.W. “Bill” Marriott Jr., chairman of Marriott International, and Richard Marriott, head of Host Hotels & Resorts, each gave $500,000 to Restore Our Future. A Marriott International spokesman said all such donations are personal and have no connection to the company.

Paulson, who made much of his fortune by betting on the housing market’s collapse, has decried the Dodd-Frank financial reform law as “a failure” and agrees with Romney that it should be repealed. He said in a statement: “We contribute to candidates and organizations that support U.S. economic growth and leadership.”

Super PACs were made possible by a 2010 ruling by the Supreme Court allowing corporations and unions to spend unlimited money on elections, yet only a handful of publicly held corporations have taken advantage of the opening so far. One of those is BE Aerospace, founded by Romney donor Amin Khoury, which gave $50,000 to Restore Our Future and has received at least $80 million in U.S. government contracts, federal data show.

The single largest known contributor in the 2012 campaign so far is Adelson, the billionaire chairman of Las Vegas Sands Corp., who gave $5 million this month to Winning Our Future, a pro-Gingrich super PAC.

The group is, in many respects, a case study of the promise and pitfalls of super PACs: Founded and funded by Gingrich’s closest confidantes, Winning Our Future has grabbed headlines for its broad assault on Romney’s time at Bain, while also prompting Gingrich to distance himself from inaccuracies in the group’s ads.

“We shifted the whole debate before we even began spending any money,” boasted Rick Tyler, a longtime Gingrich aide who now serves as senior adviser to the super PAC. “Our ads are scheduled to be interrupted only by more of our ads.”

Spokesman Ron Reese said Adelson gave money to the group because of “a long-documented personal relationship” with Gingrich. He also said Adelson does not expect any special treatment if Gingrich reaches the White House.

“He’s hopeful that Speaker Gingrich would be elected president and that maybe he would be invited to the White House Hanukkah party,” Reese said. “That’s it. There are no expectations.”

Three candidates who left the GOP race in recent weeks each had at least one super PAC championing their cause. A group favoring Rep. Michele Bachmann (Minn.) switched its support to Romney, while one backing Herman Cain has gone dormant. A spokesman for Our Destiny PAC, the pro-Huntsman group, did not respond to requests for comment on the group’s plans.

Democrats also are taking advantage of the loosened campaign finance environment. Priorities USA Action, a pro-Obama super PAC, received a $2 million donation from Hollywood mogul Jeffrey Katzenberg and $500,000 from media magnate Fred Eychaner, who co-hosted a Chicago fundraiser for Obama last week.

American Bridge 21st Century, a pro-Democratic super PAC backed by producer Stephen Bing and others, is distributing pink leaflets in South Carolina highlighting Romney’s past support for gay rights, an attempt to undermine his support among conservatives.A group called the Red, White and Blue Fund, was recently formed to bolster Santorum, who finished just eight votes behind Romney in the Iowa caucuses but lagged in New Hampshire. The group, which has bought at least $800,000 worth of ads in South Carolina, is funded in part by Foster Friess, a Wyoming-based mutual fund manager and longtime supporter of conservative and evangelical causes.

When asked what he expects in return for his financial support, which could reach $1 million, Friess joked in an interview that “I have my heart set on an ambassadorship to Zimbabwe.”

“In all my years of giving, I’ve never asked a politician for any particular favors or anything,” Friess continued. “I’ve just asked for them to support the principles of the Founding Fathers and the values that made this nation great.”

Friess added: “I do want something desperately: I want my country back.”

Staff writer T.W. Farnam contributed to this report.