WASHINGTON — The watchers are being watched.

For decades, opposition researchers have gone to great lengths to keep their names out of the public consciousness, preferring to let the fruits of their efforts — the location of a candidate's primary residence, a gaffe caught by a tracker's camera, a long-forgotten college prank — be the story.

But as some oppo research firms have increasingly come out of the shadows, they've suddenly turned their skills not on candidates of the opposite party — but each other.

Case in point: within hours of each other earlier this week Democrats and Republicans sent BuzzFeed News opposition research materials not about candidates, but literally about two opposition research firms: Democratic American Bridge and the Republican America Rising.

Opposition research can do real damage, and the two firms have produced that this cycle. A clip Rising uncovered of Iowa Democratic Senate candidate Bruce Braley dismissing a Republican senator as "a farmer from Iowa who never went to law school," has dogged him for months.

Rising and Bridge are two of the top opposition research firms, and their work has has targeted politicians up and down the ballot. Millions have been spent by candidates and parties on each firm's research, and stories about what they do dominate campaign coverage from national papers to the Lexington Herald-Leader.

Now the firms themselves are the target.

On Monday, Business Insider published a classic oppo-based story based on some blurry 2007 video purporting to show Sen. Mark Udall offering comments "That Made 9-11 Truthers Think A Senator Was On Their Side." Rising blasted the video out to its listservlistserv:

Speaking at an event in 2007, Business Insider is reporting Mark Udall made 3 comments no U.S. Senator should ever say about what happened on September 11, 2001. Udall did not immediately reject "Truther" conspiracy theories while entertaining some questions about what "really" happened on 9/11.

The hit was a flop, because it was wrong. "Here's the problem," wrote the Washington Examiner's T. Becket Adams. "When Udall's comments are put in full context, it's pretty clear that he isn't really a 'truther.'"

Udall's supporters went to work, shopping a file pointing out Rising's connections with the Business Insider story and with the National Republican Senatorial Committee, which has spent thousands on a research contract with Rising.

"When you do this kind of work and you want reporters and other political groups to use your content, your biggest asset is credibility. I'm not sure how anyone could trust America Rising after a stunt like this," the former president of American Bridge, Rodell Mollineau, said.

America Rising's executive director, Tim Miller, said Democrats are now attacking Rising because Rising has been doing so much damage to Democrats.

"American Bridge and the Democrat establishment are coming after us with unsubstantiated, garbage oppo because they are frustrated we've had real success damaging Democratic candidates this cycle," he said. "I take their attacks as a compliment."

At the same time, Republicans were at work trying to show Bridge lies.

A Republican operative went through a video shot and posted to YouTube by Bridge outside an August event for Virginia Republican congressional candidate Barbara Comstock and pulled out a six-second nugget. The Bridge tracker is heard talking to a Comstock staffer, who asks who he works for.

"I'm with American Bridge," the tracker says. "Um, and they're just a media firm out of D.C."

The Republicans labeled the clip "American Bridge Tracker Claims To Be From A Media Company" and sent it to a reporter.

Bridge spokesperson Gwen Rocco said the firm's trackers are not required to say they're Democrats.

"As is our policy, when asked our trackers identify themselves as working for American Bridge," she said when asked to comment on the video. "Given Bridge's long track record of successfully holding Republican candidates accountable for their extreme rhetoric and agenda, its no surprise we've gotten under someone's skin."

Not surprisingly, opposition researchers don't want to talk much about efforts to oppo one another. But with the high-dollar, fast-paced campaign cycle increasingly hinging on the research oppo teams produce, some of the biggest names in the practice are putting opposition research itself under the microscope.