When these stories went wrong, it was in presenting the factual dispute as a matter of the Democrats versus Romney and focusing too much on strategy, which can crowd out the substance of the campaign. A better approach would be for reporters to characterize the accuracy of ads in their own voice and to invoke non-partisan experts like PolitiFact. In some cases, it may even be possible to find credible sources on the side of the candidate airing the misleading ad who are willing to state the truth. For instance, WMUR’s Sexton briefly paraphrases a GOP strategist conceding that Romney’s ad is misleading: “Republican political strategist Mike Dennehy says it definitely appears as though Obama’s words are taken out of context.” This approach might be especially persuasive to Republicans who are inclined to trust Romney and distrust the mainstream press.

Still, it’s important to be realistic about the effectiveness of this sort of fact-checking. My co-author Jason Reifler and I have shown in our research (PDF) that fact-checking frequently fails to reduce misperceptions among the ideological group that is most likely to hold the misperception and in some cases makes the problem worse (what we call a “backfire effect”). In this case, reporters should not expect to convince skeptical readers that ads they support are false.

Nonetheless, aggressive fact-checking can provide reputational incentives (PDF) for elites to make more careful claims. For instance, after Michael Moore came under criticism in the 2002-2004 period for his misleading documentaries Bowling for Columbine and Fahrenheit 9/11, he was far more careful with the facts in 2007’s Sicko. Likewise, reporters who hold politicians accountable can help reduce their incentives to mislead the public. Doing so, however, will depend on tough coverage that convinces even the candidate’s own supporters that he or she is in the wrong—a difficult challenge, but one that more state and national journalists should aspire to meet.

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Brendan Nyhan is an assistant professor of government at Dartmouth College. He blogs at brendan-nyhan.com and tweets @BrendanNyhan.