The media is starting to agree: Donald Trump lies.

The question has instead become what to do about it during the debates.

When Trump repeated an old lie about how he opposed the Iraq War from the start of NBC's Commander-in-Chief Forum, claimed America is one the "highest-taxed" nations in the world (it's one of the least taxed), and said Hillary Clinton wants to abolish the Second Amendment (she hasn't said that), Clinton’s campaign, along with many established voices in media and politics, called for live fact-checking during the debates to counter him.

Not so fast, others argue.

Jonathan Chait at New York magazine says such a precedent would eventually kill the debates altogether. "Fact-checking sounds attractive in the age of Trump," he writes. But "Republicans aren’t going to cooperate with that, and any momentary advantage gained by weaponizing debate moderators would be lost in the next round."

Media analyst Clay Shirky has said fact-checking itself has become part of the "culture war." And as Vox’s Dara Lind pointed out, debate moderators have historically said fact-checking isn’t their role at all.

As it turns out, fact-checking experts tend to agree with Clinton’s campaign on this one: To have the highest impact, moderators should fact-check the debates live, Lucas Graves, a journalism professor at the University of Wisconsin Madison and author of Deciding What's True: The Rise of Political Fact-Checking in American Journalism, tells me.

Fully 69 percent of PolitiFact’s 260 fact-checks on Trump so far have received a "mostly false," "false," or "pants on fire" rating. By comparison, just 28 percent of the site’s 255 Clinton fact-checks have received the same. Though PolitiFact is far from comprehensive, it does demonstrate a dramatic difference between the two candidates.

Earlier in the campaign season I called up Graves to talk about fact-checking in the era of Trump. He says Trump is actually pushing journalism into a new era, emboldening newsrooms to be more aggressive in calling him out. Since then, I have followed up with him on the developments in the election and the back and forth over live fact-checking debates. Below is our conversation, lightly edited for length and clarity.

Tara Golshan: Hillary Clinton’s campaign manager, Robby Mook, has called for live fact-checking during the debates — that "if Donald Trump lies, it is pointed out." Earlier this campaign season, you also argued for real-time fact-checking during televised interviews or debates. But past moderators disagree. They say it’s the job of the politicians to engage with each other.

What are the pitfalls of moderators allowing politicians to fact-check each other?

Lucas Graves: The danger of leaving it up to the candidates to fact-check each other is that it doesn’t necessarily bring us any closer to the truth.

Politicians contradict each other constantly in speeches and commercials and debates, and the result usually isn’t very enlightening. The moderator is in a unique position to hold the debaters accountable by asking follow-up questions.

That doesn’t mean they should hit a buzzer and shout "false" whenever a candidate seems to stretch the truth. But they can point to the research that’s already out there and ask the debaters to explain if they repeat a claim that’s been debunked over and over. In a perfect world, fact-checking would be built into the debate format, so time would be set aside for each candidate to engage with some of the fact-checks that are already out there.

TG: In 2012, Candy Crowley’s live fact-check of Mitt Romney was met with backlash — people said that she had aided President Barack Obama and the debate was biased against Romney. How do you reconcile those critiques with the case for live fact-checking?

LG: If you mean substantively, I think Candy Crowley's intervention in the 2012 debate showed exactly why we need to build fact-checking into the debate format. You don't want an on-the-fly correction aimed at just one candidate. It'll be both more fair and more useful to have a mechanism where candidates know in advance that they're going to have to account for some of the major claims that fact-checkers have found wanting.

And if there's any doubt, tossing the question back to the candidate can still shed some light. Instead of flatly contradicting Mitt Romney, Crowley could have pointed out that fact-checkers had found Obama had indeed used the word "terrorism," and then invited Romney to clarify his point.

TG: What are some of the specific benefits of real-time fact-checking in debates or interviews?

LG: If candidates know they are going to be challenged on the air, they are either not going to make a misleading claim or they are going to back it up. The classic case was when Trump was fact-checked during a debate and he said, "I never said that," and they played the video evidence.

The middle of a debate or a live interview — those are the times a fact check has an impact. No politician wants to be caught with millions of potential voters watching.

One hope is that live fact-checking can actually get politicians to be more careful and to be less misleading — at least during the debate. Also, from a viewer's point of view, they are hearing the correction before the belief has a chance to take hold. There is lots of social science research to support the idea that it is much better to prevent false or mistaken beliefs from being established, because once we have established an idea we have a really hard time letting go of it.

TG: So when Matt Lauer didn’t correct Trump’s lie that he has never supported the Iraq War, what failed?

LG: What failed in that case is what usually fails. The interviewer either wasn’t prepared to dig into the specifics of what the candidates were saying or didn’t see it as part of his job.

I think it’s unfair to place all of the blame on Matt Lauer when we don’t have a strong tradition of hard-hitting political interviews on TV in this country. The bigger point is that those aren’t the qualities that networks have tended to look for in grooming their stars.

TG: From a fact-checking perspective, what makes Trump different from other candidates?

LG: If you mean why are so many people calling for fact-checking now, I think it very clearly has to do with the sense that this is an unusual election and Trump is an unusual candidate, one who flouts basic norms of public discourse and defies any sense that your rhetoric should be at least loosely based on the facts.

Trump is really unusual in his style of speech. Imagine if the race right now were between Clinton and Bush how different the political discourse would be. That is not to say that Clinton and Bush don’t exaggerate, don't mislead, or don't engage in all the routine political distortions that are a part of political life — they absolutely do — but with Trump, it is not only a question of being misleading; it is that a lot of his discourse is just free of factual claims.

He makes insinuations, he makes suggestions, he draws associations, for instance between President Obama and radical jihadists. What is the factual basis for the association? What is he actually saying about anti-American terrorists? He doesn't tell whether Obama is secretly sympathetic to them or is secretly on their side. He doesn't lay out his claims, so that makes fact-checking him a special challenge.

TG: Do you buy the idea that Trump is pushing us into some new "post-truth" or "post-fact" era? Is this campaign worse than ever?

LG: I don't agree with all of the panicky "post-truth" arguments we've been hearing, which are generally pretty ahistorical, but one positive effect is to underscore the need for journalists to do anything they can to steer political debate onto firmer ground.

I think it is impossible to measure the amount of political lying. You have really remarkable misleading claims throughout history. That feeling that we are in a "post-fact era" just reflects this long-term shift in political discourse that reflects the declining strength in parties, the end of the Cold War political consensus, and the fragmentation of the media environment.

Journalists are no longer gatekeepers in the way they were. Even a decade ago you could meaningfully speak of journalists being able to police to some extent the focus and nature of public discourse, and that is simply not true anymore. Since the 1990s, it has become easier for politicians to speak more directly to the voters, and it is easier for people to tailor their own media diet to their own preferences.

"The irony of political discourse in the age of the internet and social media is that we have never had more substantial fact-driven political discourse than we do today"

The level of analysis you see across news sites and blogs and other engaged members of the public online is fantastically elevated compared to any period in our history.

Every piece of political rhetoric is endlessly and carefully scrutinized, so people engage in substantial and factual arguments. In that sense, this is a golden age of factual discourse. But it is also easier for people to ignore the information that does not support their beliefs and for rumors to find the most receptive audience.

TG: So how is fact-checking evolving in this new era?

LG: The first thing to understand is fact-checking is the culmination of really long-term shifts in journalism: more analysis, more critical coverage, especially of political actors.

The whole idea of going behind the scenes, to analyze a political campaign strategically, only starts getting going in the 1960s. It has increased steadily since then.

Also, through the 1960s journalists had more and more examples of politicians and government officials’ willingness to lie about important matters of state. Watergate and Vietnam brought that into tremendously sharp relief. Journalists became less trusting of political officials, more skeptical of political claims.

If you ask fact-checkers, the turning point is the 1988 presidential election. The campaign was so negative and dominated by outrageous distortions [that] afterward there was a period of self-flagellation for journalists. They wondered what they did wrong, what they could have done better. There was a pretty public call for journalists to start checking the accuracy of campaign ads. Because increasingly it seemed that TV ads were really shaping the outcome of elections.

TG: How does Trump alter this dynamic?

LG: This race is another turning point in the sense that journalists are thinking pretty openly in what they have to do to deal with a candidate like Donald Trump.

You see this in their complete embrace of fact-checking — not just in a dedicated sidebar or fact-check piece but actually in the straight news reports. That has always been rare but may become more common.

TG: Are there good examples?

LG: This CNN chyron [which bluntly fact-checked a Trump remark] is something I don't think they have ever done before. Just to note in passing that a claim is not true without feeling like they have to justify it or call it a fact check or go into tremendous detail — that really reflects the unusual nature of Trump’s candidacy.

Journalists feel more comfortable challenging his claims publicly and directly. It is taken for granted that he is an unusual candidate. Pieces in the press openly compare him to demagogues in history, and he clearly has an unusual rhetorical style. That has really given journalists a kind of freedom that they haven't felt in the past to directly challenge his claims.

Another really interesting example was this Jake Tapper interview. Tapper was questioning Trump about his criticism of [federal judge Gonzalo Curiel]. Trump tried to dodge the question, as politicians usually do, and really uncharacteristically for a cable news host, Tapper really pushed back over and over and over and stayed on the same question for many minutes. That is something you almost never see in an interview with a major political candidate.

TG: Do you think this shift toward more analytical journalism and fact-checking has led to more distrust in the media? Isn’t it easier now for politicians to call out journalists for showing what they perceive as bias?

LG: Broadly speaking, the answer is no. Declining public trust in the media mirrors the decline in trust in a number of institutions in public life. It mirrors the shift away from consensus politics and party-driven politics that we have seen since the 1950s and the 1960s.

In some ways, that period in the middle of the last century — where you had widespread economic prosperity and Republicans and Democrats saw each other as the loyal opposition — was the exception. You had really high faith in public institutions.

[Since then,] our politics has become more fractured. It has become a really elemental political strategy to question the fairness of the press. The rise of the modern conservative movement since the 1960s hinged on challenging the legitimacy and impartiality of professional journalists, and that has been a very successful political strategy.

TG: Are professional fact-checkers particular targets here?

LG: It is absolutely true that fact-checking is a style of journalism that invites especially harsh partisan responses both from the public and from politicians. Fact-checkers have to weather pretty vicious responses, because they are taking a side. That is why it is so important for professional fact-checkers to scrutinize every politician — to make it clear they are independent of both parties. It is a particularly risky kind of journalism in that sense.

TG: How do you measure the impact of fact-checking in cases like Trump's? Does it make any difference?

LG: There are three different ideas for how fact-checking might make a difference.

One idea is that people might read fact checks and stop holding false beliefs.

The second idea is that fact-checking may discourage politicians from lying, because it increases the costs if they lie. There is a lot of evidence that politicians do pay attention to fact-checkers. They react loudly and angrily when they disagree with a fact check. Clearly politicians are paying attention.

The third is that it will actually change the way other journalists will report the news. If a fact check is out there, then maybe journalists won't report a false claim. They will challenge people in interviews the way Tapper did pushing back on Trump about racism.

We do see each of those models working.

TG: Is there a point of diminishing returns with fact-checking? In this case, Trump’s lies have been fact-checked over and over, and it doesn’t seem to be making a difference.

LG: It’s true that anyone who’s really paying attention has heard by now that Trump’s claim about opposing the Iraq War from the beginning was debunked, or that Clinton's statements about how she handled confidential emails have been challenged. But many people are only really starting to tune in to the election now.

Debates are a rare opportunity to assemble a large and diverse audience that crosses party lines, watching the same thing at the same time. Fact-checking is not just about spreading accurate information but about forcing politicians to account publicly for the things they say. That’s when fact-checking can really make a difference.

Watch: Donald Trump lies, but can't tell the truth