JD Vance began his assault against reality with his response to the first question in what will probably be the only vice-presidential debate of the 2024 campaign. When asked whether he would support a preemptive Israeli strike on Iran, the senator from Ohio blamed the Democratic administration of Joe Biden and Kamala Harris for the violence in the Middle East and the rest of the world. Then, he announced that, during his running mate’s one term as president, “Donald Trump actually delivered stability in the world.” Trump, Vance claimed, ”consistently made the world more secure.”

That was a jaw-dropping pronouncement about a scandal-plagued former president who cozied up to dictators, cheered on the spread of right-wing extremism across Europe, and supported vile attacks on refugees at home and abroad.

It was a laughable assertion that Democratic vice-presidential nominee Tim Walz correctly identified as “revisionist history.”

But why didn’t the moderators immediately challenge Vance and focus the debate on realistic assessments of the issues? That would not have been a radical intervention; that would have been a service to the voters, like the services performed by past moderators in previous presidential and vice-presidential debates.

The issue was that prior to Tuesday night’s debate, the moderators—CBS Evening News anchor Norah O’Donnell and Face the Nation host Margaret Brennan—made a commitment to allow Vance to lie. CBS announced that the responsibility for correcting falsehoods would fall on the candidates, though it promised the moderators would “facilitate those opportunities” to set things straight during rebuttals. O’Donnell and Brennan did try to frame the rebuttals in ways that nudged the candidates closer to the truth. But they gave Vance—a notorious fabricator, who has acknowledged making up stories about cats and dogs being served up for dinner in Springfield, Ohio—a wide lane for promoting false premises. Too wide.

Why? While CBS promised that fact-checking would occur on its live blog and social media, the moderators adopted a cautious approach in obvious deference to Republicans, who objected to ABC moderators David Muir and Linsey Davis’s correcting blatant lies by former president Donald Trump in his September 10 debate with Vice President Kamala Harris. After Trump clearly lost the debate to Harris, the former president tried to blame the ABC moderators for his failure, claiming, “We had a deal with ABC that there will be no corrections of any kind, and they violated the deal. Why? Because they’re bad people, and they’re fake news.” So furious was the Republican nominee that, within days of the debate, he was ranting, “They should fire everybody at ABC Fake News, whose two lightweight ‘anchors’ have brought disgrace onto the company!”

CBS could have stood up for the premise that journalists who moderate debates have a responsibility to the voters to call out absurd statements in real time. Instead, the network agreed to have the moderators pull their punches. That decision favored Vance, because, as Press Watch editor Dan Froomkin explained, “debates without live fact-checking are a gift to the serial liar.”

Once the debate began, Vance took full advantage of the opening CBS had given him. Author Don Winslow observed midway through the evening that “JD Vance is up there lying and lying and lying again and again and again and it’s going 95 percent unchecked. This was the road to hell in 2016.”

With the moderators stepping to the sidelines at critical junctures, Walz was at a disadvantage. While Vance lied with impunity, the Minnesotan was racing to assert the truth. New to the national debate stage, Walz stumbled a few times early in the night. But the Democrat gained traction when he challenged Vance’s lies about his previous support for a national ban on abortion and his refusal to acknowledge that Trump lost the 2020 election.