Started by President Harry S. Truman, the briefings are designed to get the candidates, before they walk into the Oval Office, up to speed on problems around the globe. Truman, who was Franklin D. Roosevelt’s vice president for almost three months before Roosevelt died, first learned about the Manhattan Project to develop an atomic bomb only 12 days into his presidency, and he pledged not to leave any future commander in chief behind the ball.

There’s an old political saw about how a White House candidate believes firmly in his or her foreign policy views — until that first top-secret briefing. In his recent book, former CIA Director Michael Hayden says these revelations are known as “aw s—” moments — as in, “Aw s—, wish we hadn’t said that during that campaign stop in Buffalo.”

If Clinton is the Democratic nominee, much of the intelligence information she receives probably will sound familiar. As secretary of state until 2013, Clinton was one of President Barack Obama’s senior advisers who were privy to the President’s Daily Brief — the highest level intelligence document prepared in the United States.

The intelligence briefings could be eye-opening for New York businessman Donald Trump. The Republican’s loose-lipped campaign remarks have left some intelligence and foreign policy officials worried about whether he can keep the nation’s secrets. Trump has said in interviews that he’s looking forward to the briefings.

Director of National Intelligence James Clapper, whose office arranges the briefings, was asked recently what he would want to say to Trump to help educate the political newcomer about foreign policy and perhaps even counter some of his ideas, such as temporarily banning Muslims from entering the United States.

Clapper bristled and said the question falsely implied that the U.S. intelligence agencies would have a separate message for each candidate.

“There’s a long-standing practice of briefing each of the candidates once they are officially designated. And that sort of shifts into higher gear, in terms of detail, after the president-elect is known,” Clapper said. “It’s not designed to shape anybody’s world view. We just brief as we normally would — each of them — and they (the briefings) have to be exactly the same.”

But Rep. Adam Schiff, the top Democrat on the House Intelligence Committee, said he believes many people share his deep concern about Trump’s inexperience with handling classified information.

“I would have to imagine that those concerns are fairly broadly held, so I wouldn’t be at all surprised if the intelligence briefings received by both candidates — which will be identical — will be at a more generalized level than they might otherwise be,” said Schiff, D-Calif.

Clinton had her own issues with secret information while secretary of state. The FBI is investigating whether her use of a private server in her home to send and receive work-related emails — including 22 that have since been classified — broke any laws.

Intelligence officials have started planning the briefings, which probably will begin right after the Democratic and Republican conventions in late July. After the Nov. 8 election, more detailed briefings for the president-elect will include information about U.S. covert operations. The sitting president has the final decision on how much information is disclosed to the president-elect; typically that includes access to the entire President’s Daily Brief.

The ritual began in 1952, when Truman offered intelligence briefings to Republican nominee Dwight D. Eisenhower and Democrat Adlai Stevenson.

CIA briefers were in a quandary after the 2000 election, when the country didn’t know for some time whether Republican George W. Bush or Democrat Al Gore had won. Bush had received a four-hour CIA briefing in September before the election at his ranch in Crawford, Texas, but he had never seen the President’s Daily Brief, which Gore saw daily as vice president.

As their lengthy ballot recount dragged into December, President Bill Clinton authorized intelligence officials to share the so-called PDB with Bush, too.

“The CIA was basically on the edges of their seats waiting for permission to start briefing Bush,” said David Priess, author of “The President’s Book of Secrets,” a history of the President’s Daily Brief.

The first one on Dec. 5 almost didn’t happen because water poured through the ceiling of the CIA’s outpost in Austin, Texas, threatening efforts to reproduce the so-called PDB on sensitive communications equipment.

Priess said Bush started receiving the PDB later than any other president in recent history, and he is the only person in the modern era to get PDB briefings before he technically was president-elect.

The pre-election briefings for Eisenhower’s successor, John F. Kennedy, raised the issue of when presidential candidates should find out about pending U.S. covert operations — in this case what became the failed U.S.-sponsored Bay of Pigs invasion meant to topple Cuban leader Fidel Castro.

Ten days after becoming president-elect, Kennedy was given the details at his family’s home in Palm Beach, Florida. Likewise, Trump or Clinton, as early as the day after the election, could learn more about operations against the Islamic State group, for instance, than they know now.

Eisenhower, the first to receive the briefings, was commander of allied forces in Europe during World War II, so he was in on his share of secrets before winning the presidency. He received four briefings, including one on a train bound for Grand Central Station in New York, according to a book by former CIA inspector general John Helgerson, who extensively researched the briefings.

Another briefing was conducted in Denver where Eisenhower stopped in at a rodeo and toured the grounds in a stagecoach with the CIA briefer riding “shotgun, up top with the driver,” Helgerson wrote.