CBS Sought the Middle Ground on Fact-Checking. Vance Jumped Into the Gap.

It was a fact-checking flashpoint.

In a tense moment at Tuesday’s vice-presidential debate, Senator JD Vance of Ohio clashed with one of the CBS News moderators, Margaret Brennan, over whether the ground rules for the evening allowed her to clarify his comments about immigrants in his home state. The pair went back and forth, and Mr. Walz started to cut in, before the network ultimately cut off both of the candidates’ microphones.

The awkward exchange may have been a result of confusion more than anything else.

The formal ground rules released by CBS News did not directly address the question of whether the moderators would unilaterally fact-check the proceedings. At the start of the telecast, Ms. Brennan and her co-moderator, Norah O’Donnell, told viewers they would offer each candidate “the opportunity to fact-check claims made by each other.”

But network executives had also indicated that the moderators may choose to clarify a fuzzy point if they determined it had been left unclear. That distinction was subtle, and the moderators did not announce it to viewers on Tuesday.

Mr. Vance jumped into that breach. He had referred to “millions of illegal immigrants” and citizens in Springfield, Ohio, whose lives, he said, were “destroyed by Kamala Harris’s open border.” Ms. Brennan responded: “To clarify for our viewers, Springfield, Ohio, does have a large number of Haitian migrants who have legal status, temporary protected status.”

Mr. Vance objected.“The rules were that you guys weren’t going to fact-check,” he said, inaccurately. “And since you’re fact-checking me, I think it’s important to say what’s actually going on.” Mr. Vance embarked on a wonky discussion of immigration law as Ms. Brennan and Ms. O’Donnell tried to cut