Will efforts to fact check Trump’s claims sway voters?

Early on in Monday's presidential debate, Hillary Clinton and Donald Trump tangled over how to combat Islamic State militants. Mr. Trump disparaged Ms. Clinton's approach to the problem, then fired off a barbed remark: "No wonder you've been fighting ISIS your entire adult life."

Ms. Clinton's response? "Please, the fact-checkers, get to work."

Mr. Trump's comment was an unnecessary piece of hyperbole easily proven false – and within moments, a small brigade of journalists had done just that. "Hillary Clinton (née Rodham) turned 18 in 1965," noted a post by Politico's Wrongometer. The Islamic State, it added, was founded in 2014, with roots in an organization created in 2004.

By now, it is clear that Mr. Trump is in a league of his own when it comes to not telling the truth on the campaign trail. That unusual penchant for falsehoods has forced media organizations to find novel and unprecedented ways of holding him to account.

Monday night's debate was a key moment in that evolution – a kind of revenge of the nerds. Media organizations deployed dozens of reporters to verify the accuracy of the candidates' claims in real time. National Public Radio marshalled a squad of journalists to produce an annotated transcript. The New York Times readied 18 beat reporters to share their expertise. Politico fired up its Wrongometer. NBC News and PolitiFact joined forces to offer a pithy breakdown of 20 false statements during the debate: 17 from Mr. Trump, the Republican nominee, and 3 from Ms. Clinton, his Democratic opponent. And the list goes on.

The crucial question, of course, is how much these efforts matter to voters. Research has shown that people are skilled at ignoring information which they don't like and often don't make political choices based on strictly rational calculations. In the coming days, a new batch of polls will emerge incorporating the post-debate period. Those surveys will provide a sense of whether the showdown – and its simultaneous fact-checking – swayed what has become a very tight race.

Researchers who have studied fact checking say that its impact on voter behaviour is difficult to determine. But just because it can't be quantified, they hasten to add, doesn't mean it isn't useful. The act of monitoring what politicians say can also change the actions of the candidates themselves by raising the reputational cost of trafficking in falsehoods.

In the 2016 presidential race, media outlets and independent fact-checking groups have encountered a candidate unlike any of his predecessors. While Ms. Clinton grapples with a perception among some voters that she is untrustworthy, she does not compete with Mr. Trump when it comes to the quantity of untruths put forward over the course of the campaign.

Interestingly, this is not a new way of doing things for Mr. Trump. Susan Mulcahy, a gossip columnist for the New York Post and Newsday in the 1980s, recently recalled how Mr. Trump differed from other publicity hounds she encountered.

Mr. Trump "wanted a lot of attention, but he could not control his pathological lying," Ms. Mulcahy wrote in Politico earlier this year. "Every statement he uttered required more than the usual amount of fact-checking. If Trump said, 'Good morning,' you could be pretty sure it was five o'clock in the afternoon."

While Mr. Trump is an unusual candidate, he is not a total departure, said Lucas Graves, a professor of journalism and mass communication at the University of Wisconsin–Madison, who has written a book on political fact checking.

"It's incorrect to say that there's some golden age in the recent past, when political discourse was guided exclusively by fact and all politicians were honest," Prof. Graves said. But there is more monitoring today. Where fact checking was "a pretty rare thing 15 years ago … it's a permanent part of the landscape now."

Already, Mr. Trump's emergence on the scene has pushed media organizations to do things differently. Back in March during one of the primary debates, Chris Wallace of Fox News presented Mr. Trump with two slides that showed the candidate's figures for how to eliminate the national deficit didn't add up. "I think it's literally the only time a graphic has gotten an ovation at a debate," Mr. Wallace later told The Washington Post.

In another first, CNN has occasionally used its chyrons – the captions that run across the bottom of a television screen – to fact check some of Mr. Trump's whoppers. "Trump calls Obama founder of ISIS (he's not)" read one such caption in August below a video of Mr. Trump speaking.

There's an "increasing willingness by journalists to fact check inside straight news reports," rather than leaving it to a column devoted solely to such monitoring, Prof. Graves said. "That's an important shift."

Earlier this month, Dean Baquet, the editor of The New York Times, confirmed that a change was under way. "We have decided to be more direct in calling things out when a candidate actually lies," he said in an interview with Quartz.

Just how the myriad attempts to hold Mr. Trump to account are influencing voters is hard to isolate. Prof. Graves said that sustained fact checking of a candidate's claim can blunt a campaign's message at critical moments. He referred to an episode late in the 2012 campaign, in which Republican nominee Mitt Romney ran a television ad in Ohio falsely claiming that a car maker was moving production to China. The ad was repeatedly debunked, draining its effectiveness.