House Republicans are seizing upon Special Counsel John Durham’s remarks to Congress regarding “outrageous” missteps during the investigation into alleged Russian collusion by President Trump in 2016 to bolster their drive to investigate perceived political bias in the federal agency — and the Justice Department more broadly.

The testimony from Mr. Durham to the House Judiciary committee on Wednesday comes as the FBI is under fire from House Republicans over the agency’s “stonewalling,” as the chairman of the House Oversight committee has put it, of congressional investigations into President Biden’s family. 

During a line of questioning from Congressman Ben Cline, Mr. Durham noted that the FBI had no legitimate basis to open the 2016 investigation into allegations of collusion between the Trump campaign and Russia because the agency did not pursue all “exculpatory evidence,” meaning evidence that helps disprove the existence of a crime, and agreed with Mr. Cline’s assessment that the FBI’s actions were “outrageous.”

Mr. Durham said he further agreed with Mr. Cline’s assertion that the FBI and its leaders failed to verify the legitimacy of certain pieces of evidence, avoided interviewing key witnesses, and abused their authority in pursuing surveillance warrants at a foreign intelligence surveillance court. 

One of the FBI’s most aggressive instances of overreach, Mr. Durham said, was when the agency received information from a foreign diplomat who spoke with a Trump campaign advisor, George Papadopulous, and then used that claim to further their investigation. Mr. Durham called Mr. Papadopulous’ claims “a suggestion of a suggestion” that did not merit further FBI investigation. 

The chairman of the judiciary committee, Congressman Jim Jordan, used his opening remarks to paint a picture of an FBI that has for years been corrupted by political actors at the top of the agency. The FBI has already gone after “parents, Catholics, journalists,” and “whistleblowers,” Mr. Jordan warned, telling the audience that “they will come for you” as well. 

Mr. Durham released a report in May that spanned more than 300 pages and asserted that there were a number of missteps made by the FBI after they launched an investigation into allegations that the Russian government had colluded with the Trump campaign, naming the operation. 

Mr. Durham previously met behind closed doors with members of the House intelligence committee on Tuesday to discuss his findings, which led many Republicans to say there was needed reform at the FBI for what they said was the existence of political bias. 

The top Democrat on the intelligence committee, Congressman Jim Himes, said following his meeting with Mr. Durham on Tuesday that he agreed there is a necessity for reform at the FBI. While Mr. Himes did not agree with the assessment that the agency is overtly politicized, he said the FBI suffered from “confirmation bias,” especially during their Russia collusion investigation. 

“I think we have found collectively that culturally and procedurally the FBI has a lot of work to do,” Mr. Himes told reporters at the Capitol. “There are all kinds of things where we need to, I think, redouble our efforts.”

Democrats on the committee relentlessly criticized Mr. Durham and his team on Wednesday for what they said was a politicized investigation of the FBI. The ranking member of the judiciary committee, Congressman Jerrold Nadler, said Mr. Durham was in search of “boogeymen” at the behest of Mr. Trump. 

Mr. Durham’s report is “Donald Trump’s one last talking point,” Mr. Nadler said. The team Mr. Durham assembled acted with “ethical ambiguity” so they could advance “Trump’s unfounded claims,” he added. The Manhattan legislator also claimed the report was nothing more than a “Defense of the Trump campaign and an attack on Hillary Clinton.”

Mr. Durham has been a federal prosecutor for more than 40 years, and served as the United States Attorney for Connecticut during both the Clinton and Trump administrations.