Robert Mueller did not need to hear Peter Strzok’s explanations. It was late July 2017, and the special counsel had summoned the F.B.I. counter-intelligence agent into his office. Mueller had recently become aware of text messages between Strzok—who was then one of the top investigators for Mueller’s probe of Russian meddling during the 2016 presidential campaign—and Lisa Page, an F.B.I. lawyer who was also assigned to Mueller’s staff. Some of the exchanges vividly bashed Donald Trump. And Strzok and Page weren’t just text buddies—they were having an extramarital affair.

Mueller swiftly delivered the news that Strzok was being removed from the Russia team. Strzok wanted to try to explain the context of the anti-Trump texts, but Mueller was not interested—not because he didn’t care whether Strzok’s political opinions might have biased the agent’s work, but because Mueller was fiercely determined to maintain both the investigation’s actual integrity and the appearance of its integrity. The existence of the texts was bad enough, no matter what was intended. Strzok, a highly respected 22-year F.B.I. veteran, left Mueller’s office headed for purgatory, a desk in the bureau’s human-resources department.

That dramatic moment emerged two weeks ago when Strzok was questioned by California Congressman Ted Lieu, a Democratic member of the House Judiciary Committee. But the testimony took place behind closed doors, and only small fragments of the nearly 11-hour-session have become public, through selective leaks. “The Republicans have been characterizing what Strzok said to make it look like Mueller didn’t care about bias,” Lieu says. “Of course he cared! He removed Strzok the minute he saw those texts!” (Mueller’s office declined to comment.)

On Thursday, Strzok will get a chance to make his case unfiltered. He will again sit for questioning by the House Judiciary Committee, this time in a public hearing, as the F.B.I. agent has requested for weeks. It would appear impossible for the 48-year-old Strzok to claim there is any nuance behind the texts where he calls Trump an “idiot” and “awful.” Two other infamous notes also seem damning: when Strzok tells Page “we’ll stop” Trump from being elected, and when Strzok tells Page, “I’m afraid we can’t take that risk [of Trump winning]. It’s like an insurance policy in the unlikely event you die before you’re 40.”

Maybe the most honest explanation is the most human: that Strzok was trying to impress Page because he was sleeping with her. Yet Lieu says Strzok has other plausible, neutral interpretations of his past words. “Look, I’m not defending what Peter Strzok did,” Lieu says. “But it’s important to hear from him because in a number of instances, people will come away viewing the texts in a different manner. Strzok doesn’t dispute that he did not like Trump. But in a number of cases, he does provide rational, credible explanations for why the texts look the way they do. For example, when he says ‘insurance policy,’ you should hear what he says about it—it’s a very different meaning than what Fox News thinks it means. And, really, the central issue is: did his personal views have any affect on the investigations? It’s very clear there’s not a single action that anyone can point to that Strzok took that reflected any bias.”

Ken Buck, a Republican congressman from Colorado who also sits on the House Judiciary Committee, scoffs at that analysis. “Strzok came across to me as a very well-prepared witness. He had clearly sat down with his lawyers. He had gone through every one of the text messages and other important historical moments, and he had very scripted answers for everything,” says Buck, who spent roughly 25 years as a district attorney and a federal prosecutor. “His explanations are not credible to me, in the sense that he does not acknowledge that personal bias can play a role in a professional decision, in how you evaluate facts and what lines of inquiry you pursue.” Asked for an example of Strzok’s bias affecting his work on Mueller’s team or in his prior role, investigating Hillary Clinton’s use of a private e-mail server while secretary of state, Buck demurs, citing the ground rules of the private testimony. Yet he is not optimistic about Thursday’s public session being much more illuminating. “I think you’ll see speeches given at the hearing, with some of the text messages or other items used as part of the overall speech,” Buck says. “And any good witness—and Strzok is a good witness—can stall for the allotted five minutes.”