A former national security adviser, John Bolton, has called President Trump “an aberration in American politics” and maintained he did not include any classified material in his 2020 memoir, amid reports that the Department of Justice could make him the president’s next adversary to face federal criminal charges.

Speaking at Harvard University’s Kennedy School of Government on Monday, Mr. Bolton, 76, said he would “love to talk about it at a greater length” but “for pretty obvious reasons” could not go into specifics about the FBI’s August 22 search for classified documents at his Bethesda home and Washington office.

“I’m very confident that there’s nothing in the book that’s classified,” Mr. Bolton told a former Department of State spokesman, Ned Price, who was moderating Monday’s hour-long talk.

During the raid, federal inspectors recovered records from his office labeled “confidential” and “classified,” including documents referencing weapons of mass destruction, diplomatic travel memos, and records of the U.S. Mission to the United Nations, according to court records. 

Published reports have suggested the FBI is investigating whether Mr. Bolton improperly sent classified information from his White House office to a home computer. 

Last week, Mr. Bolton’s attorney, Abbe Lowell, who is also representing several other Trump antagonists including New York’s attorney general, Letitia James, said the recovered documents were “cleared for his client’s use.” 

“These are the kinds of ordinary records, many of which are 20 years old or more, that would be kept by a 40-year career official,” Mr. Lowell said in a statement. 

The raid at Mr. Bolton’s home, ordered by the FBI director, Kash Patel, was described as a resumption of a “national security probe” launched in 2020 after the publication of Mr. Bolton’s book, “The Room Where It Happened,” 

The probe stems from a duel between Mr. Bolton and the Trump White House over whether he could publish the book, which he sold after his stormy departure from the White House in 2019. President Trump says he was fired; Mr. Bolton says he quit.  The White House tried — and ultimately failed — to stop the book’s publication. The Biden administration dropped the probe after Mr. Trump left office.  

On Monday, Mr. Bolton said Mr. Trump told him “it would be okay” if his book was published after the 2020 election.

“What else do you need to know?” he added. 

Mr. Bolton’s book was a no. 1 New York Times best seller and was one of the most successful Trump tell-alls, selling 780,000 copies in its first week alone. In the book, Mr. Bolton was withering about Mr. Trump, describing the president as a gullible figure easily manipulated by flattery from foreign strongmen. 

Mr. Bolton did not hold back his criticism of Mr. Trump’s handling of foreign policy during his first administration, writing in his foreword that Mr. Trump “is unfit to be President.” This enraged Mr. Trump, who referred repeatedly to Mr. Bolton as stupid, and a warmonger. The president was said to be particularly irritated that the book made Mr. Bolton a lot of money.

On Monday, Mr. Bolton continued his unfiltered criticism of Mr. Trump’s handling of foreign policy, saying “nothing disciplined his thinking” and that the president “pushed back all the time” at his advisers’ recommendations. 

The current administration is “all about Donald Trump and his neuron flashes on a day-by-day basis,” Mr. Bolton added.

“All I can say is to this day, I remain his longest-serving national security adviser,” Mr. Bolton said. He was the third of six national security advisers, so far, and, with a tenure of less than a year and a half, he did last the longest.

Last week, a former FBI director and Trump critic, James Comey, was charged with making a false statement and obstruction relating to when he testified before the Senate Judiciary Committee in 2020 that he did not authorize an FBI employee to “be an anonymous source in news reports” about the FBI’s investigations into both Mr. Trump and Hillary Clinton. 

On Truth Social, Mr. Trump applauded the indictment, calling Mr. Comey “one of the worst human beings this country has ever been exposed to.” He said Mr. Comey is now “at the beginning of being held responsible for his crimes against our nation.”

Mr. Bolton, for now, has yet to be charged with any crimes in connection with the FBI’s August 22 raid. The office of the deputy attorney general, Todd Blanche, and other senior justice department officials are pressuring the Maryland U.S. Attorney’s Office to present a case to a grand jury as early as this week, according to a Reuters report. But prosecutors are pushing back, saying more investigation is necessary, according to the report.