A former FBI lawyer has agreed to plead guilty to altering an email that helped justify surveillance of a former Trump campaign adviser as part of the 2016 investigation into Russian interference in the election, according to his lawyer and a person familiar with the matter.

Kevin Clinesmith, who worked in the FBI general counsel’s office, is expected to admit he doctored an email so it said that former Trump campaign adviser Carter Page was not a source for the CIA, even though Page previously had a relationship with the agency. Relying on what Clinesmith had said, the FBI ultimately did not disclose Page’s relationship with the CIA as it applied to renew a warrant to monitor him as a possible agent of a foreign power.

The case is the first against someone involved in the Russia probe brought by U.S. Attorney John Durham, who was tapped by Attorney General William P. Barr to broadly look into how the FBI handled that matter.

Clinesmith is hardly a household name, and the allegations against him have been known since last year, when Justice Department Inspector General Michael Horowitz issued a report excoriating the bureau for its handling of the applications to the Foreign Intelligence Surveillance Court for permission to monitor Page.

Court documents filed in the Clinesmith case do not allege a broader political or anti-Trump conspiracy within the FBI or Justice Department, and a person familiar with the matter said Clinesmith does not intend to describe any such efforts when he enters his plea. This person, like others, spoke on the condition of anonymity to discuss an ongoing case.

It was not immediately clear when Clinesmith would formally enter his plea.

President Trump brought up the expected plea at the beginning of an afternoon news conference, calling Clinesmith “a very corrupt FBI attorney who falsified FISA warrants in James Comey’s very corrupt FBI” and suggesting Durham would uncover wider wrongdoing. FISA is an acronym for the Foreign Intelligence Surveillance Act, the law under which the FBI was applying to monitor Page.

“That’s just the beginning, I would imagine, because what happened should never happen again,” Trump said.

Tim Murtaugh, his campaign’s communications director, also issued a lengthy statement alleging that the “Obama-Biden Administration weaponized the FBI and Department of Justice against their political opponent” and “undermined the peaceful transition of power.”

“Together, these abuses of power represent the greatest political crime in American history,” Murtaugh said. “Everyone involved in this plot to hurt our country must be held accountable for their corruption and perverting our democratic institutions — especially Joe Biden.”

Barr has stressed that Biden is not under investigation, nor is former president Barack Obama. Clinesmith had previously been found to have sent text messages indicating a dislike of Trump.

A lawyer for Clinesmith said: “Kevin deeply regrets having altered the email. It was never his intent to mislead the court or his colleagues as he believed the information he relayed was accurate. But Kevin understands what he did was wrong and accepts responsibility.” The expected plea was first reported by the New York Times.

The Justice Department revealed in May 2019 that Barr had tapped Durham to review the Russia probe, which Trump has derided as a “witch hunt” designed to undermine his campaign and presidency. Durham, the U.S. attorney in Connecticut, has been interviewing witnesses on a range of topics, and partisan fights about his work have intensified as the election approaches.

Republicans are hopeful Durham will condemn or charge former senior FBI officials, thereby validating their long-held skepticism of the Russia probe. In recent weeks, conservatives have grown impatient with a lack of tangible results from Durham. Democrats, meanwhile, say they fear Barr and Durham might be planning a late revelation of his findings in a way that might alter the presidential race.

To Democrats’ dismay, Barr has said he will not delay Durham’s probe because of the election. Justice Department policies call for prosecutors to not take actions for the purpose of affecting an election, and by tradition, law enforcement generally avoids taking steps that could have that appearance. But Barr has said the rules do not apply to Durham’s investigation because he is not investigating political candidates.

On Thursday, Trump seemed to take a veiled swipe at his attorney general, telling Maria Bartiromo of Fox Business, “Bill Barr has the chance to be the greatest of all time, but if he wants to be politically correct, he’ll be just another guy, because he knows all the answers, he knows what they have, and it goes right to Obama and it goes right to Biden.”

Barr appeared on Fox News on Thursday evening and seemed to try to placate Republican concern over the pace of Durham’s probe, telling host Sean Hannity there would be “significant developments before the election.” He said that one development would come Friday but that it was not “earth-shattering.”

Barr has previously said that Durham is mainly focused on uncovering criminal wrongdoing but that he expects “there will be public disclosure in some form of report.”

Durham’s investigation and other reviews of the Russia probe also have raised Trump’s ire toward FBI Director Christopher A. Wray, who the president suggested Thursday could be “more forthcoming.” The FBI said in a statement Friday that the bureau “has been, and will continue to be, fully cooperative with Mr. Durham’s review,” including by assigning personnel to help him and by providing documents to his team. The FBI noted that Clinesmith had resigned before an internal disciplinary process could be completed.

Horowitz, the inspector general, had first exposed Clinesmith’s alleged wrongdoing in a 2019 report in which he examined the applications to surveil Page and other aspects of the Russia probe. He detailed a spate of troubling errors that showed officials repeatedly emphasized damaging information about Page while downplaying any material that suggested his innocence.

Among the failures was what the bureau told the court about Page’s relationship with another U.S. government agency, and what an FBI lawyer relayed internally about that relationship. Horowitz’s report does not name the agency or the lawyer, but people familiar with the matter have said they are the CIA and Clinesmith.

The agency had told the FBI in August 2016 that it had a relationship with Page. That was before the bureau applied to monitor him. In the spring of 2017, when Page was under surveillance, he asserted publicly that he had worked in the past with the CIA.

In June 2017, an FBI agent working on the application to renew the warrant to surveil Page decided he wanted a “definitive answer” on whether Page had been a CIA source. If he had been, that might undercut the notion that he was working for a foreign power.

Clinesmith, according to Horowitz’s report and people familiar with the matter, got in touch with a CIA liaison, who indicated in an email that Page had a relationship with the agency of some sort.

According to the criminal information filed Friday detailing the allegations that led to Clinesmith’s planned plea, Clinesmith wrote to the FBI agent that the CIA liaison “confirmed explicitly” that Page was never a source of theirs. When the agent asked if they had that in writing, Clinesmith said yes and forwarded him the liaison’s email indicating some type of relationship, but he added the phrase “not a source.” Clinesmith had separately provided the unaltered email to a different Justice Department attorney.

Clinesmith “did willfully and knowingly make and use a false writing and document,” the information said.

Page said in a statement Friday that Clinesmith was “finally being held accountable and pleading guilty to committing a felony for his involvement in the plot to falsely portray me and by implication the Trump Administration as traitors.”

“Clinesmith, his organization and their associates put my very life at risk, leading to abusive calls and death threats because of my personal opinions and support for President Trump,” Page said. “There is a long way to go on the road to restoring justice in America, but certainly a good first step has now been taken.

Following intelligence reports highlighting concerns election security, Democrats and Republicans disagreed on Aug. 9 over who poses the greater threat. (The Washington Post)

In 2018, then-Rep. Mark Meadows (R-N.C.), now the White House chief of staff, publicly named Clinesmith as the lawyer referred to only as “FBI Attorney 2” in a separate inspector general report documenting the FBI investigation of Hillary Clinton’s use of a personal email server.

Horowitz found that the lawyer, who was the primary FBI attorney assigned to the Russia probe in its early days, sent multiple instant messages indicating a strong dislike of Trump, including one saying, “Viva le resistance.” Clinesmith insisted to Horowitz’s investigators that many of them were jokes and that he did not let his political views affect his work.

Meadows tweeted Friday, “One down, hopefully several more to go.”

Horowitz’s report concluded that the bureau had an “authorized purpose” to initiate the investigation into Russian interference in the 2016 election and possible coordination with the Trump campaign. Page was only a part of that inquiry, and Horowitz has said he did not find evidence of the problems there “infecting” the rest of the probe.

But Horowitz has said he was concerned that the FBI did not reevaluate its examination of Page, particularly as agents failed to uncover wrongdoing and wondered among themselves why they were still investigating the former Trump campaign adviser.

Durham has said he disagrees with some of Horowitz’s findings on the cause the FBI had to open the 2016 investigation.

In questioning witnesses, Durham’s investigators have shown particular interest in why the bureau kept pressing forward after it came to have doubts about the credibility of Christopher Steele, a former British intelligence officer whose work the FBI relied on in part to obtain the secret court order to surveil Page, people familiar with the matter said.

Investigators were particularly interested in doubts raised about Steele by one of his sources of information, according to these people.

Barr told Fox News host Mark Levin this week that Durham has “a sprawling number of issues” to examine, though he did not elaborate.

“There are a lot of different conspiracy theories, and part of our responsibility is to look at all of these things so we can assure people that these various theories have been looked at, and so this takes some time,” he said.

Rosalind S. Helderman and Spencer S. Hsu contributed to this report.