Moderating a presidential debate is one of the hardest jobs in American journalism. A mere seven people have fulfilled that role over the course of 19 debates held between 1988 and 2012.

The rest of us have no idea what it takes. Tens of millions of Americans tune in to watch the political equivalent of the Super Bowl. And, as with any sporting event, much of the rage from both sides will end up directed at the ref.

This year, the ref has to preside over a face-off between one candidate so careless with the facts to have inspired a cottage industry of articles announcing the "post-truth" era and another so guarded with the facts that she is with her rival the most distrusted candidate in at least 20 years.

One question has loomed largest over the first debate, to be held tonight at 9 p.m. Eastern, moderated by NBC's Lester Holt. A question dissected every which way from media commentators. Even the Hillary Clinton and Donald Trump campaigns have weighed in forcefully.

The question is, of course: Should the moderator fact-check the candidates?

The Candy Crowley conundrum

Setting aside the (to me, ludicrous) argument that it is up to the candidates to fact-check one another, there are good reasons for moderators' reluctance to correct the candidates.

The standard example brought up by the "no fact-checking" side is the 2012 debate moderated by then-CNN host Candy Crowley. And yet it is an imperfect example.

Crowley was in a tight spot. She was called upon to intervene by President Obama on a question of semantic nuance: How did he characterize the Benghazi attacks on the day after? Moreover, GOP candidate Mitt Romney had botched his punch line, using "act of terror" instead of "terrorism," allowing Obama to be technically right but contextually misleading.

The Washington Post Fact Checker has a good play-by-play of that spat and it takes several minutes to wrap one's head around it. Good fodder for on-air fact-checking, this isn't.

Top fact-checkers agree. "The Crowley example was difficult, because Obama's words after Benghazi were intentionally nuanced," says PolitiFact editor Angie Holan. "It was one of those things where it wasn't that clear-cut, but on the other hand, if you were going to explain what the issue really was, you would have to take a significant diversion."

Glenn Kessler, of the Post's Fact Checker, is less diplomatic. "That's a good example of when the moderator tried to fact-check and got it wrong. Obama was engaging in revisionist spin."

Overall, Kessler is wary of live fact-checking during the debate by a moderator. "People who are watching the debate want to see how the candidates answer, react, they really don't care about the moderator."

A more convincing fact check by the moderator came in February, during the South Carolina GOP primary debate. In discussing the Supreme Court seat left vacant by the late Antonin Scalia, Ted Cruz argued that "We have 80 years of precedent of not confirming Supreme Court justices on an election year."

Dickerson tried, politely, to highlight that Cruz should have said nominated rather than confirmed (he wasn't himself crystalline about the historical context). Cruz fumbled, Dickerson apologized, the audience booed.

Holan says Dickerson "cued to the audience that something wasn't right," but whether the finer points about Supreme Court history were understood is anyone's guess.

Moderators' hesitation to jump in on nuanced subjects is appropriate, she said. Eugene Kiely, director of, agrees: "the credibility of moderator and fact-checker is on the line" during a presidential debate.

Fact-check sparingly, fact-check differently

But that kind of nuance hasn't exactly been front-and-center during this campaign. The current debate over the role of moderators as fact-checkers began anew this month after "Today" host Matt Lauer let Donald Trump get away with the widely debunked claim that he was against invading Iraq from the start.

Nuance was also absent when, in one of the first GOP primary debates, Trump accused moderator Becky Quick of fabricating an attack on Marco Rubio — an attack which was on Trump's website all along.

Even if Quick had persisted, it probably wouldn't have been an election-changing fact check. But it could have provided future moderators with a model for rolling out simple, indisputable on-air corrections.

Egregious falsehoods, such as Trump's slight against Rubio, ought to be called out. "The moderator shouldn't sit there like a potted plant while a candidate says something that is obviously inaccurate," says Holan.

Kiely says moderators could also push the candidates to be more factual without resorting to full on-air fact-checking. For instance, they could pose questions built around false statements from the campaign trail. In addition, Kiely says, they should mention the correct number if a candidate uses an outdated statistic — as Mike Pence has been doing with poverty numbers — then quickly move on.

Beyond raising issues of fact, moderators can needle the candidates into exposing flaws in their arguments by pushing them to clarify their point, says Kessler. In the 1976 debate, Max Frankel of The New York Times was probably more effective as a bemused panelist repeating President Ford's statement that "there is no Soviet domination of Eastern Europe" back to him, than as a fact-checker.

(Debate lore says the gaffe lost Ford the election, but we didn't fact-check that.)

If fact-checkers had a magic wand

Reality aside, what would the debate look like if the fact-checkers had a free hand to determine the format?

"My ideal is that after each segment you let fact-checkers come up for 15 minutes and let the moderators ask follow-up questions based on that," says Holan. "I think candidates need to be fact-checked close to when they make the claims," which is when they are fresher in voters' minds.

Kiely is more cautious, concerned that inserting fact checks into the debates could perversely give viewers the false notion that everything that wasn't directly challenged was correct.

For Kessler, it might worth doing a lightning round at the end with five statements fact-checkers have rated as false from the campaign, similar to what Glenn Thrush has proposed.

But we shouldn't imagine that fact-checking in the debate will sway the election, Kessler says. "The American people don't cast their votes on the basis of the person who makes the most accurate statement [...] American presidential elections are often based on emotions, guts, whether you'd get a beer with that person, whether you 'like' them. It's a much more personal vote than in other democracies."

Kiely suggests an alternative to fact-checking by the moderator. "Just have the networks doing more fact-checking after the debate," he says. As currently stands, "they spend more time discussing who won and who lost among people who have vested interests. Who cares!"

With the Commission on Presidential Debates unlikely to change things much in this sense, Kiely suggests injecting fact-checking in the coverage, rather than the format, of the debate.

That would be one place to start; but it would require action from many more people than just the moderator.

And who doesn't like to blame their own failings on the referee?