WASHINGTON — The embattled F.B.I. agent who oversaw the opening of the Russia investigation mounted an aggressive defense of himself and the F.B.I. on Thursday, rejecting accusations that he let his private political views bias his official actions and labeling Republicans’ preoccupation with him “another victory notch in Putin’s belt.”
“Let me be clear, unequivocally and under oath: Not once in my 26 years of defending my nation did my personal opinions impact any official action I took,” the agent, Peter Strzok, told House lawmakers investigating what Republicans say is evidence of rampant bias at the top levels of the F.B.I.
But in defending himself and his agency, Mr. Strzok had to weather hours of blistering attacks by Republicans, who accused him not only of personal animus toward President Trump but also of blatant lying and moral misconduct with a senior F.B.I. lawyer, Lisa Page.
It was a remarkable day of shouting matches and personal attacks that showcased the deep partisan divide over the federal investigation into whether the Trump campaign colluded with Russia to influence the outcome of the 2016 election. The performance by Republicans, echoing Mr. Trump’s own lines of attack, demonstrated just how far many in the party have moved since the days when they were seen as the party of law enforcement, deferential to its power and prerogatives.
Democrats, on the other side of the now-gaping divide over the F.B.I. and Justice Department, said that Republicans, by launching their own politically motivated investigation of the investigators in an attempt to bolster Mr. Trump, were ignoring an attack by a hostile foreign power on American democracy.
The public comments were Mr. Strzok’s first since volumes of private text messages between him and Ms. Page were disclosed in a report by the Justice Department’s inspector general that found no evidence that their personal views had swayed their work on the Hillary Clinton email case. The agent concluded his opening remarks on Thursday with a pointed broadside against his antagonizers.
“I understand we are living in a political era in which insults and insinuation often drown out honesty and integrity,” Mr. Strzok said, continuing: “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.”
He concluded: “As someone who loves this country and cherishes its ideals, it is profoundly painful to watch and even worse to play a part in.”
The fiery hearing, convened by the House Judiciary and Oversight Committees, devolved into a spectacle almost as soon as it began, as pent-up rage between House Republicans and the F.B.I. broke into the open in spectacular fashion, including with an almost immediate threat to hold Mr. Strzok in contempt of Congress after he said the F.B.I. had barred him from answering certain questions.
As the hearing stretched deep into the afternoon, it broke into pandemonium when Representative Louie Gohmert, Republican of Texas, invoked Mr. Strzok’s extramarital affair with Ms. Page to question his character.
“I can’t help but wonder when I see you looking there with a little smirk, how many times did you look so innocent into your wife’s eye and lie to her?” he said.
Democrats shouted that the statement was “intolerable witness harassment.” Representative Bonnie Watson Coleman, Democrat of New Jersey, demanded, “Do you need your medication?”
Mr. Strzok, visibly irked, insisted that he had “always told the truth” and shot back that Mr. Gohmert’s invocation of “a family member who I have acknowledged hurting goes more to a discussion about your character and what you stand for.”
Republicans were intent on painting Mr. Strzok as seething with contempt for Mr. Trump and his supporters — and by implication, painting the agency’s investigation of the president as motivated by animus.
“He thinks calling someone destabilizing isn’t bias,” said Representative Trey Gowdy of South Carolina, the chairman of the House Oversight Committee, referring to texts sent by Mr. Strzok. “He thinks protecting the country from someone he hasn’t even begun to investigate isn’t bias. He thinks promising to ‘stop’ someone he is supposed to be fairly investigating from ever becoming president isn’t bias.”
Mr. Gowdy dismissed Mr. Strzok’s defenses, saying that the agent had a “most unusual and largely self-serving definition of bias” that had undermined the fair administration of justice.
To a surprising extent, Mr. Strzok appeared just as intent on defending the F.B.I.’s actions, the integrity of the Russia investigation that continues under Robert S. Mueller III and his own behavior.
“At every step, at every investigative decision, there were multiple layers of people above me, assistant director, deputy director, director of the F.B.I., and multiple layers of people below me, section chiefs, unit chiefs and analysts, all of whom were involved in all of these decisions,” he told Mr. Gowdy after the chairman pressed him. “They would not tolerate any improper behavior in me any more than I would tolerate it in them.”
“The suggestion that I, in some dark chamber in the F.B.I., would somehow cast aside all of these procedures, all of these safeguards and do this is astounding to me,” he said. “It couldn’t happen.”
For their part, Democrats tried to run interference for Mr. Strzok, using parliamentary points of order and other tactics to protect him from Republican prying. One Democrat, Representative Steve Cohen of Tennessee, said Mr. Strzok deserved a Purple Heart.
“All of these inquiries about your political opinions as revealed by these text messages are irrelevant and wrong, unless it can be shown — as it has not been shown, as was found definitively not to be the case in the Hillary investigation and has not been shown in the Russia investigation — that they affected any decisions in the investigation,” Representative Jerrold Nadler of New York, the top Democrat on the Judiciary Committee, told Mr. Strzok.
Instead, Democrats accused Republicans of attacking a veteran F.B.I. agent to divert attention from Russia’s effort to promote the election of Mr. Trump.
“There is a criminal investigation into the Trump campaign and possible crimes related to the 2016 presidential election involving collusion with Russian spies to sell out our democracy and hijack the presidency,” said Representative Hakeem Jeffries, Democrat of New York. “My colleagues in the cover-up caucus don’t like that criminal investigation, and therefore, they need to identify a villain. Mr. Strzok, tag, you’re it.”
Mr. Strzok, a career agent, played a pivotal role in two of the bureau’s most politically fraught cases in recent memory: the investigation into Mrs. Clinton’s email practices as secretary of state and a separate inquiry into Russia’s election interference. He briefly served on Mr. Mueller’s team, as well, before being removed after the discovery of his text messages with Ms. Page.
In one oft-cited exchange from August 2016, Ms. Page, who also worked on both investigations, said to Mr. Strzok that Trump was “not ever going to become president, right?”
“No. No he won’t. We’ll stop it,” Mr. Strzok replied.
Mr. Strzok said on Thursday that he deeply regretted the messages, but that they did not amount to more than private political beliefs. He defended that particular text as a late-night, “off-the-cuff” message after “then-candidate Trump” insulted “the immigrant family of a fallen war hero,” Humayun Khan.
“And my presumption, based on that horrible, disgusting behavior” was “that the American population would not elect somebody demonstrating that behavior to be president of the United States,” he said.
He added that a broader look at his texts would show disparaging remarks toward all the candidates in the 2016 campaign.
“To suggest we can parse down the shorthand like they’re some contract for a car is simply not consistent with my or most people’s use of text messaging,” Mr. Strzok said.
House Republicans were not placated by such explanations, and repeatedly instructed Mr. Strzok to read select text messages aloud, amid other questions about prosecutorial decisions in the Clinton case and his interactions with Mr. Mueller.
“What does Trump support smell like?” Representative Robert Goodlatte of Virginia, the Judiciary Committee chairman, asked, referring to one message in which Mr. Strzok wrote that he could “SMELL” Trump supporters in a southern Virginia Walmart.
A former Army officer, Mr. Strzok has worked at the F.B.I. for more than two decades. He rose quickly through its ranks, earning a reputation within the bureau as one of its most savvy and reliable counterintelligence agents. It was that reputation and increasingly senior positions that landed him on the teams investigating both Mrs. Clinton and eventually Mr. Trump.
The report on the Clinton case issued last month by the Justice Department’s inspector general was unsparing in its criticism of Mr. Strzok and Ms. Page, but found no evidence that their personal views had affected prosecutorial decisions in the case. The inspector general, Michael E. Horowitz, continues to investigate the F.B.I.’s handling of key aspects of the Russia case.
The committees have also demanded testimony from Ms. Page, issuing a subpoena for her to appear in private for an interview and threatening her with contempt when she did not meet that deadline. Lawyers for Ms. Page said she was happy to testify, but only after the F.B.I. allowed her to review her notes and relevant case files. After two Republican chairmen issued an ultimatum on Wednesday, Ms. Page was scheduled to take part in a private deposition on Friday and Monday.