It's possible the fact-checkers are intentionally or unintentionally letting some bias show through. Whether or not that's true, the state of each party right now most certainly plays a role. A lot of very conservative Republicans got elected in 2010, and the Tea Party got a lot of attention, and some Tea Party Republicans have had a tendency to say inflammatory things. Like, say, Michele Bachmann.
Rival fact-checker Glenn Kessler of The Washington Post noted on Tuesday that with Bachmann's retirement, he'll lose some of his best material: "As one of our colleagues put it, 'The entire fact checking industry may have to hold a national day of mourning.'" In 2013 Bachmann has earned four Pinocchios, the most false rating the Post offers. Over her career, PolitiFact rated 15 Bachmann claims to be "pants on fire" ratings, its harshest rating. PolitiFact called her retirement "shocking."
Bachmann was a fact-checker's dream because she was prominent, she got lots of attention, and she didn't mind throwing out easily disprovable statistics. But she's only a four-term member of Congress from Minnesota, and she doesn't have an important leadership role in the House. Nevertheless, she was elevated to national stardom by the cable news appearances that offered fact-checkers so much great material. And that helped her launch a presidential campaign.
Democratic Rep. Yvette Clarke was elected the same year as Bachmann, 2006. But PolitiFact didn't bother with Clarke when she went on The Colbert Report in September 2012 and said that Brooklyn still had slavery in 1898, five decades after New York abolished slavery, and three decades after the Civil War ended. "Slavery. Really? I didn’t realize there was slavery in Brooklyn in 1898," Colbert responded. "I'm pretty sure there was," Clarke said.
PolitiFact did not rate this claim. There are some obvious reasons why — Clarke is a little-known congresswoman; her claim was not about a current policy debate. Bachmann, on the other hand, was a presidential candidate.