Today politicians anticipate being “PolitiFacted,” as Rick Perry and Jeb Bush have both put it recently, verbifying the Pulitzer Prize-winning site run by the Tampa Bay Times. For a candidate, the delight in those moments when a fact-checker skewers an opponent is rarely tempered by the reality that they too will eventually find them selves in the same fact-checker’s unsparing gaze.

“If you get a good ruling, you can swing it like a cudgel at your opponent through the entire campaign,” one senior state Republican in Virginia told me. “And there’s little if any defense.”

In fact, fact-checking can be such a powerful weapon that campaigns are increasingly launching their own partisan fact-checkers, aping the journalists’ style, language and presentation in ads, news releases and social media postings. Just this week, Correct the Record—a group formed by David Brock as a “rapid response team” to defend Democratic presidential candidates from “right-wing, baseless attacks”—announced it was spinning off from its parent PAC in order to work more directly in support of Hillary Clinton’s campaign.

Clinton will hardly be the first candidate to circumvent the press with an overtly partisan fact-checking operation not dependent on the facts as the press sees them. But the blurring line between the work of journalists and their partisan doppelgangers seriously undermines media fact-checking’s ability to serve the political players who matter most—the voters.