Plenty of half-truths (and outright non-truths) were uttered during the Clinton-Trump debate last week, and Tuesday's Kaine-Pence head-to-head saw outright denial of statements that had been made on the record - and on camera.
ABC's Martha Raddatz and CNN's Anderson Cooper, who will moderate the second presidential debate on Sunday, face a sizeable challenge. Will they manage to respond correctly to any lapses in truth-telling by the candidates?
One man has some advice for them.
Joe Navarro estimates that he conducted 13,000 interviews while working for the FBI, during which plenty of people tried to mislead him.
Before his retirement in 2003, he also taught advanced counterterrorism interview techniques for the bureau. The man knows how to weed out the truth: so what does he think?
1) Language really matters (including body language)
"The difficult thing about lying is we all do it, and we have all done it from a very early age," Navarro says. "As a species, we are very deceptive - if you want your mother's attention, you might pretend you hurt yourself."
The way a sentence is framed may hint whether a lie is being peddled, but so may the way it is delivered.
"If you ask a question, does it cause some sort of psychological discomfort, and if it does, how does it manifest in the body?
"The body reveals in real time your psychological discomfort. Do they purse their lips? Do they begin to touch their neck? Do they increase their smoking?"
Neither candidate is likely to light up, though - neither smokes, and all buildings at Washington University in St Louis, which is hosting the debate, are no-smoking zones.
2) Tease out the lie, and cut them off
"What we tried to do is to start with open questions," says Navarro, now an author and public speaker. "'What's your experience of this?' 'What do you think about this?' You hold back that which you are certain about.
"I would allow them to say whatever they want, and once they have said it, cut them off sharp and say 'No, that is not accurate, that doesn't match up with the truth, and here's why.'
"By cutting them off sharp, what in essence you are doing is putting them at a psychological disadvantage that they, thus far, have not had."
3) Know your facts, and ignore the clock ticking
"You don't want to create an atmosphere - but journalists have a responsibility not to tolerate nonsense. At some point, you have to make clear you are not going to tolerate this and that this is a serious session."
One suggestion Navarro has is for the moderators, when presented with a lie, to insist on not moving forward until that fact is clarified. Doing so would shake up the candidates keen to say as much as possible while the clock is ticking.
"Such a dramatic challenge would be revolutionary," he says.
4) Manage an angry response
"You have to remember, when you are dealing with high-status individuals there is a lot of narcissism, self-entitlement and being used to not being challenged, putting other people down," Navarro says.
"Even the most favourable ones have some of that. Confront them with the facts. With narcissists, they don't know how to handle that, so they come back with rage. The smart person will try to find another answer.
"But what I have found is that moderators are ill-prepared with the facts to make the challenge, and that they are worried about fighting the clock."
The key, Navarro says, is to not be ruled by emotion - the calmest person is likely to come out on top.
"The moderators will be as much on trial as the candidates themselves. People are wondering what they are going to tolerate."