Mr. Baier's aggressive demeanor was consistent with the kind of tough coverage of Ms. Harris that blankets Fox News's daily programming. Lots of viewers were surely eager to hear how she would respond when confronted head-on.

Frequently, however, Mr. Baier did not give viewers that chance. Instead, looking frustrated, he cut off several of Ms. Harris's answers after a few seconds. His first interruption came within the first half-minute of their exchange.

"May I please finish responding?" Ms. Harris asked at one point. "I'm in the middle of responding to the point you're making, and I'd like to finish."

A veteran interviewer, and the face of Fox News's relatively nonpartisan 6 p.m. newscast, Mr. Baier was eager to shake Ms. Harris off her usual talking points, including playing a Trump campaign ad and asking her to respond.

Still, in his eagerness to prevent a filibuster, Mr. Baier's follow-up questions sometimes resembled rebuttals.

"We feel like we definitely achieved what we set out to achieve, in the sense that she was able to reach an audience that has probably been not exposed to the arguments she's been making on the trail," Brian Fallon, Ms. Harris's campaign communications director, told reporters on Air Force Two. "She also got to show her toughness in standing tall against a hostile interviewer."

Mr. Trump has refused to participate in another debate with Ms. Harris - even on Fox News ... For now, Mr. Baier's grilling on Wednesday evening may have to stand in.