Harry Truman had been vice president for only 82 days when Franklin Roosevelt died, so there was quite a lot he needed to learn when he became president in 1945. “He didn’t even know the atomic bomb existed,” historian David Priess said. “He didn’t know about the Manhattan Project.”

Director of National Intelligence James Clapper told reporters at a recent breakfast that the top-secret briefings would take place at a secure facility, whenever the candidates request. He was pressed about how his office would be sure the information in its presentations would stay secure.

The process is set up “to ensure that everybody gets the same information,” Clapper said, “and that we do comply with the need to protect sources and methods and comply with security rules.”

Priess, a former CIA officer and author of The President’s Book of Secrets, a history of the president’s daily brief, said that experience made Truman resolve that no future president should come into office unprepared.