WASHINGTON (AP) — President Harry S. Truman, who became president on April 12, 1945, upon the death of Franklin D. Roosevelt, didn't learn about the Manhattan Project to develop an atomic bomb until his 12th day in office. Vowing never to leave another president uninformed, Truman began the practice of giving presidential nominees intelligence briefings to prepare them for the demands of the job. A look at how some of them went:

DWIGHT D. EISENHOWER

Unlike Truman, who had little exposure to U.S. intelligence agencies, Eisenhower had been privy to U.S. secrets in his job as Supreme Commander of the Allied Forces in Europe during World War II. Still, he received four briefings before the 1952 election while campaigning around the country, and more after becoming president-elect.

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JOHN F. KENNEDY

Eisenhower approved the covert U.S.-backed Bay of Pigs invasion meant to topple Cuban leader Fidel Castro, which was planned throughout the 1960 campaign. Cuba came up in CIA briefings that Kennedy received after becoming the Democratic nominee, but he didn't get the covert details of the plan until 10 days after the election.

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RICHARD M. NIXON

As vice president for eight years, Nixon was well-schooled in intelligence matters.

Two days after he won the 1968 Republican presidential nomination, he and his running mate, Spiro Agnew, flew to President Lyndon B. Johnson's ranch in Texas to get a CIA briefing. Before the briefing — Nixon's only one before the general election — Johnson gave them a tour of his ranch in a convertible.

After the election, the CIA compiled briefing materials for the president-elect in the basement of a building at 450 Park Avenue in New York. After complaints of a rat infestation, health inspectors demanded admission. They were turned away.

Intelligence officials sent briefings to Nixon in sealed envelopes marked "Eyes Only-The President-elect," but some came back unread. Nixon had no one-on-one briefings with the CIA as president-elect, although the agency's information was getting to Nixon through his national security adviser, Henry Kissinger.

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JIMMY CARTER

Carter was the first presidential candidate to ask for and receive intelligence briefings before he clinched the nomination. CIA officials quickly learned that a sod airstrip in Carter's home of Plains, Georgia, could not accommodate the agency's Gulfstream plane. The plan then was to land at an Army airfield in Fort Benning, Georgia, and take a helicopter to what they were told was "Peterson Field." That turned out to be just a field owned by a farmer named Peterson.

During some of the briefings Carter received before becoming president, he would sometimes spin a globe next to his chair. Intelligence officials played with Carter's daughter, Amy, and her cat. President Gerald Ford authorized the briefings, which were done by then-CIA Director George H. W. Bush. He was cleared to discuss the logistics of intelligence briefings that Carter would receive after being nominated, but they ended up talking about a range of intelligence issues before his nomination was official.

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RONALD REAGAN

Reagan's only pre-election intelligence briefing was on Oct. 4, 1980, at a borrowed country estate near Middleburg, Virginia.

Participants described the briefing as a "circus" with people constantly coming and going from a room scattered with chairs. Historians said that Reagan, known as a delegator, was probably trying to get his aides involved in the process.

That year, the CIA also provided intelligence briefings to third-party candidate John Anderson.

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BILL CLINTON

Clinton also received only one intelligence briefing before the general election. CIA Director Robert Gates traveled to Little Rock, Arkansas, to brief him on Russia, the conflict in the former Yugoslavia, Iraq, weapons of mass destruction and hunger in Africa.

After he became president-elect, Clinton received the more detailed briefing. One day, Clinton, who was hurriedly tying his necktie and drinking a Diet Coke, asked his briefer to give him the highlights. But Clinton decided the subject matter was too interesting to dismiss and plopped down and read the entire brief before leaving.

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GEORGE W. BUSH

During the campaign, Bush was given a four-hour extensive CIA briefing at his ranch in Crawford, Texas. One CIA officer demonstrated how a terrorist could use a briefcase to release chemical or biological weapons — a prop Bush soon ordered out of the room.

After the 2000 election, Clinton administration officials didn't know quite what to do about briefing the president-elect because there wasn't one. Republican Bush and Democrat Al Gore were in a hotly contested ballot recount. As vice president, Gore was already reading the President's Daily Brief, but Bush was not.

The Clinton administration decided to make Bush the first presidential candidate in history to receive the President's Daily Brief before becoming the official president-elect.

After the Supreme Court upheld Bush's victory, the briefings during the transition continued in Austin, Texas.

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BARACK OBAMA

After the 2008 Democratic convention, Obama asked for and received one briefing, which covered terrorism and related topics, but not covert operations. GOP nominee Sen. John McCain also had a briefing.

After the election, President-elect Obama was to start receiving more sensitive intelligence information, but there was a mix-up. Intelligence briefers were ready to brief him in Chicago, starting with a few overview sessions. But Obama was under the impression that all his advisers would be briefed.

The intelligence officers said they wouldn't give it to anybody without the necessary security clearances. Obama ended up accepting one solo briefing, but said that until the clearances were arranged, he would just read the President's Daily Brief instead of getting a briefing. Eventually it was agreed that after Obama's inauguration the advisers would be looped in after they were appointed to positions that made them eligible to see it anyway.

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Source: "The President's Book of Secrets" by David Priess and historical research by former CIA inspector general John Helgerson