But that does not make Comey a criminal, legal analysts said.
"He can fairly be criticized for whether that was the best way for him to address his discomfort with his conversation with the president," said Barry J. Pollack, a white-collar criminal-defense attorney at Miller & Chevalier who has been involved in leak cases. "But that's all a matter of how he conducts his job, and what his relationship is with the president is not a legal question."
Prosecutors who bring charges against people for sharing information with the public can do so only when classified or other national security material is at issue. Material cannot be classified to conceal legal violations or prevent embarrassment, according to an executive order from President Barack Obama. Telling a reporter nonclassified information of public interest is not only legal, but it's often the right thing to do.
"I think, on balance, this is one of these extraordinary circumstances where the issues are so important, that what Comey did and his acknowledgment that he did it is understandable and in his mind necessary, and he did something that I think is courageous," said Jeffrey H. Smith, a former CIA general counsel now in private practice at Arnold & Porter.
Comey told the Senate Intelligence Committee he did not share classified material.
By Comey's account, Trump — after a meeting in the Oval Office — cleared the room of other officials, isolating the two of them, and said of Flynn: "He is a good guy. I hope you can let this go."
At the time, the FBI was investigating Flynn for his contacts with Russians and possibly lying to government investigators about them. Trump and his lawyer have disputed that the interaction occurred as Comey described.
Comey said that he meticulously documented his interactions with the president, and he asked a friend to share the content of his memo about Flynn with a reporter, "because I thought that might prompt the appointment of a special counsel" in the probe of Russian meddling in the 2016 election. He said he did not reveal the information personally "because I was worried the media was camping at the end of my driveway at that point . . . and I worried it would be like feeding sea gulls at the beach if it was I who gave it to the media."
The maneuver was one of a veteran Washington power player — shielding Comey, at least temporarily, from any personal scrutiny about the information. Pollack said that, while not illegal, Comey's action belied his public persona.
"I think Mr. Comey had publicly always presented himself as somebody who does things by the book, and I think it's pretty hard to argue that leaking something to the New York Times through an intermediary so you don't leave any fingerprints on it is what most people would consider by the book," Pollack said.
But it achieved Comey's goal. The day after the New York Times published an article about Trump's request on Flynn, Deputy Attorney General Rod J. Rosenstein appointed former FBI director Robert S. Mueller III to serve as special counsel overseeing the Russia probe.
Trump's lawyer, his supporters and even the president himself have hammered Comey for his admission. The lawyer, Marc E. Kasowitz, said in a statement that Comey's talks with Trump were "privileged communications with the President" and referred to their release as "unauthorized disclosures."
A person close to the president's legal team said they were preparing to file a "complaint" early next week with the Senate Judiciary Committee and the Justice Department Office of the Inspector General — which can investigate criminal matters and also prepare public reports on current or former employees suspected of misconduct. A spokesman for the office declined to comment.
Trump has previously suggested on Twitter that he might have tapes of his encounter with Comey, and he told reporters who asked about them Friday, "I'll tell you about that maybe sometime in the very near future." He offered later, "You're going to be very disappointed when you hear the answer, don't worry."
Meanwhile, legislators continued their push to access Comey's memos. Comey told the Senate Intelligence Committee on Thursday that he had turned over his copy to Mueller, although he said that his friend, Columbia Law School Professor Daniel C. Richman, might still have the memos and that he would encourage him to release them.
Richman declined to provide the materials or comment to The Washington Post on Friday. The FBI declined to say whether they have copies of the memos at all, and a spokesman for Mueller declined to comment.
Federal records law prevents the removal or destruction of government documents — but that is generally meant to protect the documents, and analysts said they doubt Comey ran afoul of that rule.
"I'm not suggesting it's a good thing to leak. I think it's abhorrent conduct," said Shannen W. Coffin, a former Justice Department official and counsel to Vice President Richard B. Cheney. "But in terms of a criminal prosecution, I find that hard to imagine in this context."
At the same hearing in which Comey admitted engineering a leak, he said the "importance of aggressively pursuing leaks of classified information" was "a goal I share."
The context of his leak, of course, is different: By his account, none of the information he shared was classified. But legal analysts noted that those who leak often claim a pure motive — and prosecutors often discount them.
"To me, the guy who oversaw the most leak investigations and prosecutions of any administration in American history decides to become a leaker when it suits his own interests?" said defense attorney Edward B. MacMahon Jr., who represented a former CIA officer convicted in a leak case. "The irony is quite rich."
David Nakamura contributed to this report.