The recent buzz that one of the frontrunners to be Republican presidential contender Mitt Romney's vice presidential pick, Sen. Rob Portman of Ohio, had registered as a foreign agent for the Duvalier dictatorship in Haiti came from American Bridge 21st Century, a super PAC that's spent most of its money not on attack ads, but on opposition research.

The registration was old news: A July 17 Washington Post profile of Portman, seen at right, noted it, along with a Patton Boggs attorney's statement that, though registered, Portman hadn't represented Haiti. But it shows that independent expenditure groups can influence elections even without doing huge ad buys. American Bridge did far more than post Portman’s 1985 foreign lobbying disclosure form--they compiled a 347-page book of Portman opposition research and published it online, part of Veepmistakes.com, a collection of unflattering dossiers on potential Romney running mates.

The focus on digging up dirt reflects the background and expertise of American Bridge 21st Century's founder, David Brock, who first gained fame in the 1990s by writing about accusations of sexual infidelity that surrounded President Bill Clinton for the American Spectator, a conservative magazine. He made a dramatic about-face in 1997, when he published in Esquire his “Confessions of a Right-Wing Hit Man,” and went on to ply his talents on behalf of the left -- first as CEO of Media Matters, which criticizes conservative commentators in general and Fox News in particular, and now at American Bridge.

While other super PACs have spent the bulk of their money on media buys, the biggest expense for American Bridge is staff. Of the $6.2 million American Bridge has spend so far this year, expenditures for salary and payroll tax account for more than half: $3.8 million. Records show 71 salaried employees across several states. Some of these employees shadow candidates to record gaffes. The New York Times has written about these “trackers” and the centralized video archive they are creating.

As of June 30, the super PAC had raised $8.6 million. A 501(c)4 affiliate that does not have to identify donors because of its tax status, American Bridge 21st Century Foundation, has given its sister organization $500,000 in offsets to operating expenditures this cycle.

American Bridge digs up dirt on opponents, makes the research public and lets the media or other campaigns advertise their findings. Former research director Shauna Daly described her job as "leading the largest research and tracking information in politics, providing the basis for independent expenditure paid media and rapid response in presidential, Senate and House races." Daly was a veteran of President Obama's 2008 campaign. American Bridge president Rodell Mollineau is a former spokesman for Senate Majority Leader Harry Reid, D-Nev.

This is part of an increasingly sophisticated division of labor for groups that can’t officially coordinate with the candidates they support.

"A giant research and tracking effort," is how Chris Harris, the communications director of American Bridge, describes the project. The idea is to be a centralized entity that can provide research (often, as the GOP veep candidates' dossiers demonstrate, opposition research) for Democratic candidates up and down the ballot. "We know the Democratic outside groups will not match Republican dollar to dollar. We need to be smarter, more strategic and more efficient," Harris says. "Part of efficiency is cutting down on duplication. If American Bridge did not exist, all organizations would have to hire their own researchers."

(Jacob Fenton contributed to this story.)