The investigation into President Trump’s former national security adviser, John R. Bolton, began to pick up momentum during the Biden administration, when U.S. intelligence officials collected information that appeared to show that he had mishandled classified information, according to people familiar with the inquiry.
The United States gathered data from an adversarial country’s spy service, including emails with sensitive information that Mr. Bolton, while still working in the first Trump administration, appeared to have sent to people close to him on an unclassified system, the people said, speaking on the condition of anonymity to discuss a sensitive case that remains open.
The investigation of Mr. Bolton, who has become an ardent critic of the president, burst back into public view last week when federal agents searched his Maryland home and Washington office.
While those searches have raised fresh questions about the extent to which Mr. Trump may be using the Justice Department and F.B.I. to try to punish those he dislikes, the new details of the case present a more complex chain of events. The disclosures suggest that a long-running investigation into Mr. Bolton’s activities changed over time, with some of the issues echoing past inquiries into the handling of national security secrets.
The emails in question, according to the people, were sent by Mr. Bolton and included information that appeared to derive from classified documents he had seen while he was national security adviser. Mr. Bolton apparently sent the messages to people close to him who were helping him gather material that he would ultimately use in his 2020 memoir, “The Room Where It Happened.”
In a sign of the stakes for Mr. Bolton, he is in talks to retain the high-profile criminal defense lawyer Abbe Lowell. Mr. Lowell, who has represented Mr. Trump’s son-in-law, Jared Kushner, and Mr. Biden’s son Hunter, is defending two other prominent perceived enemies of Mr. Trump who are now under scrutiny: the New York state attorney general, Letitia James, and Lisa Cook, a member of the Federal Reserve Board.