“The combination of factors just wasn’t present with either President Bush or President Obama,” he said.

— Matt Apuzzo

Comey orchestrated a leak

Mr. Comey acknowledged that he orchestrated the leak that revealed his account of his conversation with Mr. Trump in which the president asked him to drop the investigation into the former national security adviser.

Mr. Comey said he decided to make the conversation public through an intermediary after Mr. Trump said on Twitter that the former F.B.I. director had better hope there were no tapes of their discussions. He said he did so with the explicit hope of prompting the appointment of a special counsel to investigate Russian election interference.

“I woke up in the middle of the night on Monday night, ‘cause it didn’t dawn on me originally that there might be corroboration for our conversation; there might be a tape,” Mr. Comey said, referring to May 15. “And my judgment was I needed to get that out in the public square so I asked a friend of mine to share the content of the memo with a reporter. Didn’t do it myself for a variety of reasons but I asked him to because I thought that might prompt the appointment of a special counsel. So I asked a close friend of mine to do it.”

An article about the memo was published online by The New York Times on May 16, and in the newspaper the next day. The story attributed the information to “two people who read the memo” without naming them.

Questioned by Senator Susan Collins, Republican of Maine, Mr. Comey did not identify the friend by name but said he is a professor at Columbia University. Daniel Richman, a law professor at Columbia, confirmed Thursday that he was the close friend who served as intermediary.

— Peter Baker

‘Not a witch hunt’