NEW HAMPSHIRE — Last Tuesday, the New America Foundation released a report (PDF) I co-authored with Georgia State’s Jason Reifler on how to most effectively combat misperceptions (summarized here at CJR). Two days later, some of the nation’s press corps decided to illustrate what not to do instead.

The occasion was the implausible claim by Joe Arpaio, the controversial and high-profile sheriff of Maricopa County in Arizona, that President Obama’s birth certificate is a forgery. The claim was covered by Politico, the Associated Press, the New York Post, The Arizona Republic, and discussed on the cable news networks.

Beyond the political freak show aspect of the event, what’s the news here? Obama’s long-form birth certificate was released last April, confirming the authenticity of his previously released “certification of live birth” and contemporaneous birth announcements in two newspapers. No credible evidence has emerged since then to raise any questions about his citizenship. So why would we believe Arpaio could possibly hold such evidence? As National Review’s Kevin D. Williamson wrote, “If you expect us to believe that there was a conspiracy — originating before the birth of Barack Obama — involving the Honolulu newspaper, local and state governments, the White House, foreign regimes, and National Review, and that said conspiracy remained undocumented until Sheriff Joe’s Maricopa County Irregulars sleuthed it out, you are asking a lot.” Would reporters cover an Arpaio press conference in which he claimed to provide evidence that the moon landing was faked?

In addition, Arpaio is not a credible messenger. He is known for media grandstanding and is cooperating with Obama’s Department of Justice after an investigation found “grave misconduct” in the sheriff’s office. In addition, it quickly emerged that the “lead investigator” in Arpaio’s “Cold Case Posse” is selling an e-book based on his “findings” that was co-authored with conspiracy theorist Jerome Corsi.

More importantly, coverage of Arpaio’s claims has the potential to do quite a bit of damage. As Reifler and I show in our report, repeating falsehoods can create a feeling of fluency that causes people to misperceive them as true over time. Also, if people come to believe Arpaio, the effects are difficult to undo. Misperceptions are difficult to correct (PDF) and can have persistent effects on subsequent opinions and attitudes.

These concerns are especially serious given the resilience of the birther myth. A recent YouGov survey conducted by MIT’s Adam Berinsky suggests that public doubts about Obama’s citizenship are on the rise again. Berinsky found that the percentage of Americans agreeing that Obama was born in this country increased from 55% before the release of the birth certificate to 67% immediately afterward (including an increase from 30% to 47% among Republicans). However, a late January poll he conducted found that belief that Obama was born in the US had receded to 59% overall and 27% among Republicans. Coverage of Arpaio’s claims has the potential to accelerate this trend.

With all that said, some journalists may believe it is necessary to cover Arpaio’s statements given his stature as a public official. For instance, The Arizona Republic’s J.J. Hensley told CJR’s Erika Fry last week that the newspaper was aware of the risks of reinforcing misperceptions but felt an obligation to report on the press conference given Arpaio’s prominence within the state. Hensley noted that it was not possible for him to provide technical refutation of Arpaio’s claims with the time or resources that were available to him so he focused on “the political theater aspect” of the event.

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