FBI official Peter Strzok testified defiantly on Thursday that he was not biased while investigating 2016 election candidates, but said at the same time that he disapproved of then-candidate Donald Trump's "horrible, disgusting behavior."

Strzok won applause from Democrats during a joint hearing of the House oversight and judiciary committees after offering an explanation for an August 2016 text message to then-FBI attorney Lisa Page that "we'll stop" Trump from being president.

"I think its important when you look at those texts that you understand the context in which they were made and the things that were going on across America," Strzok testified.

"In terms of the the text that 'we'll stop it', you need to understand that that written late at night off the cuff, and it was in response to a series of events that included then-candidate Trump insulting the immigrant family of a fallen war hero, and my presumption based on that horrible, disgusting behavior that the American population would not elect somebody demonstrating that behavior to be president of the United States," he said.

"I do not have bias," he added at another point in the hearing.

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The discovery of Strzok's messages with Page, with whom he was having an extramarital affair, resulted in his 2017 removal from special counsel Robert Mueller's investigation of possible Trump campaign collusion with Russia.

Strzok oversaw the opening of the FBI's original election-related Russia investigation in July 2016, after playing a leading role in the FBI investigation of Hillary Clinton's use of a private email server to communicate classified information, softening the wording of a statement by then-FBI James Comey to describe her conduct.

Strzok, transferred last year to the FBI's human resources division, told lawmakers Thursday that multiple layers of staff at the FBI would prevent personal bias from improperly influencing the direction of investigations.

Regarding the "we'll stop it" text, Strzok continued: "It was in no way, unequivocally any suggestion that me, the FBI, would take any action whatsoever to improperly influence the electoral process. There are multiple layers of people above me... and multiple layers of people below me."

"They would not tolerate any improper behavior in me any more than I would tolerate it in them," he said. "The suggestion that I in some dark chamber somewhere win 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."

"And the proposition that that is going on, that it might occur anywhere within the FBI, deeply corrodes what the FBI is in American society the effectiveness of their mission and it is deeply destructive," he concluded.

Democratic lawmakers applauded.