Glenn Kessler for WaPo:

At the Fact Checker, we have often said we do not write fact checks to change the behavior of politicians. Fact checks are intended to inform voters and explain complicated issues.

Still, most politicians will drop a talking point if it gets labeled with Four Pinocchios by The Fact Checker or “Pants on Fire” by PolitiFact. No one wants to be tagged as a liar or misinformed, and we have found most politicians are interested in getting the facts straight. So the claim might be uttered once or twice, but then it gets quietly dropped or altered.

But the news media now faces the challenge of Donald Trump, the presumptive Republican nominee for president. Trump makes Four-Pinocchio statements over and over again, even though fact checkers have demonstrated them to be false. He appears to care little about the facts; his staff does not even bother to respond to fact-checking inquiries.