What kind of moderator will Fox’s Chris Wallace be?

Chris Wallace, the “Fox News Sunday” anchor who is moderating tonight’s debate, declared over the weekend that his job “is to be as invisible as possible.” But his well-received turn as a moderator in 2016 hinged on the opposite.

It was Mr. Wallace’s subtle but firm presence that guided Donald J. Trump and Hillary Clinton to what was widely viewed as the candidates’ most substantive encounter of the 2016 campaign. Mixing humor with scolding, Mr. Wallace posed some sharp queries while taking pains to defuse chaotic moments.

“I’m not a potted plant here,” Mr. Wallace said at one point when the candidates’ bickering threatened to drown him out. “I do get to ask some questions.”

His most memorable moment came on a subject that is almost certain to crop up again on Tuesday: election integrity. Mr. Wallace repeatedly pressed Mr. Trump on whether he would accept the election results, a pledge that the Republican candidate refused to make. “I will keep you in suspense,” was Mr. Trump’s defiant reply.

The first Fox News anchor to take charge of a general election debate, Mr. Wallace faced skepticism from some Democrats, who were unimpressed with his questions about Mrs. Clinton’s lucrative paid speeches to banking firms. Republicans balked when Mr. Wallace bluntly asked Mr. Trump why “so many different women, from so many different circumstances,” had accused him of sexual misconduct.

Those who know Mr. Wallace say they expect him to be an equal-opportunity interrogator on Tuesday. One thing he is unlikely to do, however, is fact-check Mr. Trump and Mr. Biden in real-time. “I do not believe it is my job to be a truth squad,” Mr. Wallace said while preparing for his first debate go-round in 2016. “It’s up to the other person to catch them on that.”