FBI counterintelligence agent Peter Strzok will tell lawmakers today that despite a trove of text messages from 2016 that seem to indicate he had an intense personal distaste for President Donald Trump, he has never allowed personal opinions to affect any of his official work at the agency.

“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,” Strzok will testify before a joint panel of the House Judiciary and Oversight and Government Reform Committees, The Associated Press reported.

Strzok will tell lawmakers in his prepared opening statement that he followed department protocol handling sensitive information about the extent of Russia’s meddling in the U.S. election and the Trump team’s potential role in it.

“This information had the potential to derail, and quite possibly, defeat Mr. Trump,” Strzok will say. “But the thought of exposing that information never crossed my mind.”

The hearing Thursday will mark Strzok’s first public testimony about his involvement in the 2016 investigations into possible ties between the Trump campaign and Russia and Hillary Clinton’s use of a private email server.

The longtime FBI agent helped lead both the Trump campaign and Clinton email investigations at various points in 2016 and was later part of special counsel Robert S. Mueller III’s probe into the Trump campaign’s ties to Russia.

Republicans in Congress have railed against Strzok for months after an extensive series of texts from 2016 between Strzok and his mistress, Department of Justice lawyer Lisa Page, emerged in which the Strzok said “we’ll stop” a Trump presidency.

Strzok was removed from Mueller’s team when those messages went public.

Lawmakers from the committees questioning Strzok Thursday interviewed him behind closed doors in June.

If GOP lawmakers’ questions Thursday resemble those from the closed-door interview last month, Republicans are prepared to unleash on Strzok with a slate of searing questions that touch on his alleged extramarital affair with Page, what kind of access he had to a dossier on Trump’s ties to Russia prepared by former British intelligence agent Christopher Steele, and whether he voted for Republicans or Democrats in 2016.

The DOJ’s inspector general concluded in a report released last month that department officials committed numerous indiscretions over the course of the Trump campaign investigation in 2016.

But IG Michael Horowitz “did not find documentary or testimonial evidence that improper considerations, including political bias, directly affected those specific investigative decisions,” he told the House Judiciary Committee on June 19.

Watch: How Trump’s Attacks on Mueller Probe Are Playing on Capitol Hill