But Mr. Brock, the founder and chairman of Media Matters, makes no secret of the candidate he favors in the election: he hosted two fund-raisers recently that, he said, raised $50,000 for Mr. Obama. And John D. Podesta, a former chief of staff to President Bill Clinton who helped create Media Matters, is a chairman of the team that would facilitate Mr. Obama’s transition to the White House, should he win.

“I’m a good progressive,” said Mr. Brock, who also gave money to the primary campaign of Senator Hillary Rodham Clinton.

Though its sleek, glassed-in offices here on Massachusetts Avenue resemble the former law firm that once occupied them, the team of researchers search for the kind of “gotcha” moment that the organization might publicize.

“The local guys are harder to listen to,” said Julie Millican, 26, who oversees the transcription and analysis of more than a dozen radio programs, from Michael Savage and Mr. Limbaugh to Chris Baker of KTLK-FM in Minneapolis and Dan Caplis of KHOW-AM in Denver. Ms. Millican said local hosts “will go off and spend 20 minutes talking about a pothole in the neighborhood. The next thing you know, they’re calling Hillary Clinton a”  and here Ms. Millican used a vulgarity.

Each morning at 9:30, several dozen researchers and editors gather in a low-ceilinged conference room for their “edit call,” in which they essentially pick their shots. On a recent morning, they decided to take aim at Mr. Savage, the radio host who reaches an estimated eight million listeners a week, for saying that “the only people who don’t seem to vote based on race are white people of European origin.” He made his comment after suggesting that “B.O.,” as he calls Mr. Obama, was endorsed by former Secretary of State Colin L. Powell “because of his race.”

Whether Media Matters has affected the course of the 2008 election  by intimidating some reporters or commentators, or forcing a change in the tone of others  is difficult to judge, with no shortage of blogs now trying to do some version of what it does.

One of its most concerted campaigns was to cast doubt this summer on the veracity of “The Obama Nation,” a book by Jerome Corsi. In a live interview on MSNBC with the author, Contessa Brewer cited “some 8, 9, 10 pages of factual errors” unearthed by Media Matters, and then asked Mr. Corsi, “Why should we give you the credibility?”