“Agent Strzok had Hillary Clinton winning the White House before he finished investigating her,” said Representative Trey Gowdy, Republican chairman of the House Oversight and Government Reform Committee. “Agent Strzok had Donald Trump impeached before he even started investigating him. That is bias.”

Strzok repeatedly insisted that the texts, including one in which he called Trump a “disaster,” did not reflect political bias and had never infected his work. He said the FBI’s Trump investigation originated not out of personal animus but rather from concern that Russia was seeking to meddle in the election, including what he said were credible allegations of a Russian offer of assistance to a Trump campaign associate.

He made clear his exasperation at being the focal point of a congressional hearing when Russian election interference has been “sowing discord in our nation and shaking faith in our institutions.”

“I have the utmost respect for Congress’s oversight role, but I truly believe that today’s hearing is just another victory notch in Putin’s belt and another milestone in our enemies’ campaign to tear America apart,” Strzok said.

The hearing underscored a little-discussed reality of law enforcement and government: agents and federal workers hold deeply held political views but are expected to keep them out of their work.

Strzok insisted that separation was possible. “What I am telling you is I and the other men and women of the FBI, every day take our personal beliefs, and set those aside in vigorous pursuit of the truth – wherever it lies, whatever it is.”

To which Republican Representative Ted Poe responded: “And I don’t believe you.”

Strzok said under aggressive questioning that a much-discussed August 2016 text in which he vowed “we’ll stop” a Trump candidacy followed Trump’s denigration of the family of a dead US service member. He said the text, written late at night and off-the-cuff, reflected his belief that Americans would not stomach such “horrible, disgusting behaviour” by the presidential candidate.

But, he added in a raised voice and emphatic tone, “It was in no way – unequivocally – any suggestion that me, the FBI, would take any action whatsoever to improperly impact the electoral process for any candidate. So, I take great offence, and I take great disagreement to your assertion of what that was or wasn’t.”

Plus, he said in an animated riff that drew Democratic applause, both the Clinton and Russia investigations were handled by large teams that “would not tolerate any improper behaviour in me any more than I would tolerate it in them.

“That is who we are as the FBI,” he said. “And the suggestion that I, in some dark chamber somewhere in the FBI, would somehow cast aside all of these procedures, all of these safeguards and somehow be able to do this is astounding to me. It simply couldn’t happen.”

The hearing exposed clear partisan divides in the House judiciary and oversight committees, as Democrats accused Republicans of trying to divert attention from Trump’s ties to Russia through an excessive focus on Strzok.

Democratic Representative Steve Cohen of Tennessee said he would give Strzok a Purple Heart if he could. And Representative Bonnie Watson Coleman said, “I have never seen my colleagues so out of control, so angry.”

But Republicans eager to undermine Mueller’s investigation berated Strzok, holding up the texts as evidence of partisan bias within a law enforcement agency meant to steer clear of political considerations. An inspector general report blamed Strzok and FBI lawyer Lisa Page for creating an appearance of impropriety through their texts but found that the outcome of the Clinton investigation was not tainted by bias.

At one point, Representative Louis Gohmert, a Texas Republican, invoked Strzok’s personal life by alluding to the fact the texts were exchanged while he and Page were having an affair. “When I see you looking with a little smirk, I wonder how many times did you look so innocently into your wife’s eyes and lie to her about Lisa Page,” Gohmert began.

The hearing room erupted, with someone shouting “insane asylum” and someone else asserting that Gohmert needed medication.

The comments sparked immediate objections from Democrats, who called them outrageous, and Strzok was livid. He told Gohmert the fact that he would say that to him “shows more what you stand for” than anything else. Gohmert tried to shout over him and the committee chairman vainly tried to restore order.

The hearing was punctuated by chaos and yelling as Judiciary Committee Chairman Robert Goodlatte said Strzok needed to answer Republicans’ questions and suggested they might recess the hearing and hold him in contempt. Democrats objected to Goodlatte’s repeated attempts to get Strzok to answer. Goodlatte eventually let the hearing proceed without calling the panel into recess.

In his opening statement, Strzok acknowledged that while his text message criticism was “blunt”, it was not directed at one person or political party and included jabs not only at Trump but also at Clinton and Senator Bernie Sanders.

He said he was one of the few people during the 2016 election who knew the details of Russian election interference and its possible connections with people in the Trump orbit, and that that information could have derailed Trump’s election chances.

“But the thought of exposing that information never crossed my mind.”

FBI Director Chris Wray says employees who were singled out for criticism in the report have been referred to internal disciplinary officials. Strzok’s lawyer has said he was escorted from the FBI building as the disciplinary process winds its way through the system.

Additional reporting by The Washington Post