Attorney Michael Sussmann departs a federal courthouse after opening arguments in his trial in Washington on May 17, 2022.
CNN  — 

A former top FBI official testified Thursday that he is “100% confident” that Hillary Clinton campaign lawyer Michael Sussmann told him he wasn’t providing a tip about Donald Trump’s potential ties to Russia on behalf of the campaign or any client, critical testimony that bolsters special counsel John Durham’s claims that Sussmann illegally hid his political ties.

Former FBI general counsel James Baker, Durham’s most critical witness, told a jury in Washington, DC, about his September 2016 meeting with Sussmann, where Sussmann passed along the tip about Trump.

Sussmann has pleaded not guilty to one count of lying to the FBI – specifically that he falsely told Baker he wasn’t there on behalf of any clients.

“He said he was not appearing before me on behalf of any particular client, and that he had some information that was of concern relating to an apparently surreptitious communications channel between something called Alfa Bank – which he described as being connected to the Kremlin in Russia – and some part of the Trump Organization in the United States,” said Baker, a former CNN legal analyst.

The FBI looked into the Trump-Alfa tip and determined within weeks that “there was nothing there,” Baker said. One of the central theories of Durham’s case is that Sussmann brought the tip to Baker on Clinton’s behalf, but concealed his campaign ties as part of a scheme to dupe the FBI into investigating Trump, and then to gin up an “October surprise” about it in the press.

On the witness stand, Baker said he “trusted” Sussmann’s claim that he was there on his own because they were friends, and he knew Sussmann as “a serious lawyer” who worked for the Justice Department and had cybersecurity expertise needed to understand the Trump-Alfa data.

“I thought he was coming to see me as a good citizen who had obtained some information,” Baker testified. “Knowing Michael, I would think he would want to help the government.”

Baker’s testimony could give a boost to Durham, the Trump-era special prosecutor who has spent three years investigating potential misconduct in the FBI’s Trump-Russia probe. He hasn’t delivered any of the bombshell indictments that Trump has hoped for, and the Sussmann trial is the first major courtroom test of his inquiry, which has brought charges against three people.

But the verdict could turn on how jurors assess Baker’s credibility. Sussmann’s lawyers tried to chip away at that with a meandering cross-examination that highlighted how Baker’s answers to key questions shifted when testifying to Congress in 2018, to the Justice Department watchdog in 2019, in his many interviews with Durham’s prosecutors, and on the witness stand this week.

Defense attorney Sean Berkowitz got Baker to acknowledge that it was actually the prosecutors who “triggered my memory” of what happened six years ago at the Sussmann meeting. Baker said that when he met with prosecutors in recent years, they refreshed his recollection by asking pointed questions and showing him notes that an FBI official wrote about their conversations.

Judge rules against mistrial

Earlier on Thursday, Judge Christopher Cooper rejected Sussmann’s request for a mistrial.

Lawyers for Sussmann had argued Wednesday that he can’t get a fair trial because one of the witnesses suggested Sussmann could answer a key question by testifying in his own defense, violating his constitutional rights. The witness was Marc Elias, who served as the top lawyer for Clinton’s campaign, and was otherwise a relatively helpful witness for Sussmann’s defense.

Prosecutors called Elias to the stand, but it was the defense attorneys who spurred him to make the comment in question. They asked if he knew whether Sussmann brought the Trump-Alfa tip to Baker “on behalf of the (Clinton) campaign.” Elias replied, “You’d have to ask Mr. Sussmann.”

Cooper ruled form the bench against a mistrial Thursday morning, but he approved Sussmann’s request to strike some of the problematic portions of Elias’ testimony from the court record.

The defense lawyers also said Sussmann hasn’t decided whether he’ll testify in his own defense. They are preparing to put on a defense case with a handful of fact witnesses and character witnesses.

This story has been updated with additional details.