Sept. 8, 2011 -- President John F. Kennedy was so "worried for the country" about the prospect that Vice President Lyndon Johnson might succeed him as president that he'd begun having private conversations about who should become the Democratic Party's standard-bearer in 1968, Jacqueline Kennedy recalled in a series of oral-history interviews recorded in early 1964.

She said her husband believed strongly that Johnson shouldn't become president and, in the months before his death in November 1963, he'd begun talking to his brother, Robert Kennedy, about ways to maneuver around Johnson in 1968.

"Bobby told me this later, and I know Jack said it to me sometimes. He said, 'Oh, God, can you ever imagine what would happen to the country if Lyndon was president?'" she said.

The president gave no serious consideration to dropping Johnson from the ticket in 1964, Jacqueline Kennedy recalled. But he did have some talks about how to avoid having Johnson run for president in 1968, at the end of what would have been Kennedy's second term, she said.

"He didn't like that idea that Lyndon would go on and be president because he was worried for the country," she said. "Bobby told me that he'd had some discussions with him. I forget exactly how they were planning or who they had in mind. It wasn't Bobby, but somebody. Do something to name someone else in '68."

Watch the two-hour Diane Sawyer Special "Jacqueline Kennedy: In Her Own Words" Tuesday 13 at 9:00 p.m. ET on ABC.

Jacqueline Kennedy's recollections, in a series of interviews conducted by writer-historian Arthur M. Schlesinger Jr. and kept private by the Kennedy family until this month, depict a distant and at times disturbing relationship between a president and the man who ultimately did succeed him in office upon his assassination.

The tapes are illuminating not just for the words but for how they're spoken, the distinctive, breathy voice – at times wistful, at times wickedly irreverent – revealing a new dimension of woman who carefully kept herself out of the public eye. With sounds of matches striking, ice cubes clinking, and even her children playing in the background, it's a rare snapshot into the life and private recollections of Jacqueline Kennedy.

They also detail under-the-surface tension that lingered between Jacqueline Kennedy and her husband's successor. That tension stood in sharp contrast to the famous image of a blood-spattered on her standing at Johnson's side as he took the oath of office aboard Air Force One, hours after President Kennedy was killed in Dallas.

ABC News' Diane Sawyer will host a prime-time, two-hour special based on the tapes Sept. 13, featuring exclusive audio of Jacqueline Kennedy's interviews. The transcripts are being released in book form this month in "Jacqueline Kennedy: Historic Conversations on Life with John F. Kennedy."

Johnson served more than six years as president, filling out Kennedy's term and then getting elected in his own right in 1964. While his White House years were largely defined by the escalation of the Vietnam War, he was able to pass landmark civil rights legislation that had been started and stalled under Kennedy. He also launched ambitious domestic projects, including the War on Poverty and "Great Society" legislation that created programs such as Medicaid, Medicare and Head Start.

Click Here to Travel Back in Time With the Kennedys Through ABC News' Interactive Timeline

Caroline Kennedy, the child of John and Jacqueline Kennedy, told Diane Sawyer that when it comes to her mother's thoughts on President Johnson, the tapes capture a complex moment in time.

"It's funny because she was really fond of Lyndon Johnson, and really loved Lady Bird, and always stayed in touch with her and they would visit," she said.

"The description of Lyndon Johnson here is more of his capabilities as a president, more negative than she certainly felt about him as a person," she continued. "I think she really appreciated the efforts that he made for her, when she was leaving the White House, and towards me and John -- and she found him really amusing and warmhearted. And I think that it's interesting because she's able to separate those human qualities from some of his shortcomings as president.

"I also think that there's stuff going on -- again, this is a moment in time -- between him and Uncle Bobby. That is probably coloring her opinion here."

But on the tapes, Jacqueline Kennedy describes a vice president who was far from the inner sanctum of power. She describes a lieutenant who resisted the president's efforts to solicit his input and involve him, even in areas that interested him.

"Jack would say you could never get an opinion out of Lyndon at any cabinet or national security meeting," she said. "Lyndon, as vice president, didn't just do anything. But it was all right. It was fine."

As vice president, Jacqueline Kennedy said, Johnson "was never disloyal," she said. But she added that he seemed interested in "the panoply that goes with power, but none of the responsibility."

When they were fellow senators in the late 1950s, Johnson's profanity and political trickery "sort of amused" Kennedy, Jacqueline Kennedy said. She said the future president "didn't particularly like him."

By Jacqueline Kennedy's telling, her husband never really wanted Johnson on his 1960 ticket in the first place. She said he really wanted to choose Missouri Sen. Stuart Symington, and even indicated that Symington was his choice to a mutual friend, Clark Clifford, on the day of his nomination at the Democratic National Convention.

In choosing among possible running mates in 1960, Kennedy and his close allies "liked Lyndon Johnson the least," Jacqueline Kennedy said. But Kennedy believed he needed to offer Johnson a spot on the ticket "to annul him as majority leader," she said, fearing that his "enormous ego" would have led Johnson to block Kennedy's agenda in the Senate as president if he felt slighted.

"Everyone was even amazed that he accepted," she said. "Some other people can tell you about it, going down into his room and everything -- and I guess he was drunk, wasn't he?"

Recorded in early 1964, Kennedy was seeking to shape her late husband's legacy at the same time that the new president was adjusting to the office in which he was suddenly thrust. She fretted that Johnson was currying favor with FBI Director J. Edgar Hoover, whom her husband, she said, planned to oust after the 1964 election.

That decision was among several that have "all been done the wrong way" under President Johnson, Jacqueline Kennedy said.

She depicted the new president as struggling with the burdens of the office, saying "the poor man's terrified" and appeared "panic-struck."

In a prescient observation about Vietnam -- the comments came in June 1964, years before the Vietnam War descended into the quagmire that would sink the Johnson presidency -- she warned that the new president's leadership style left him ill-equipped to handle the deepening crisis in Southeast Asia.

"Jack always said the political thing there was more important than the military and nobody's thinking of that," she said. "And they don't call the people who were in it before. And so that's the way chaos starts."

Apparently realizing how her tone sounded, she added, "people will think I'm bitter, but I'm not so bitter now. But I just wanted it to be in context the kind of president Jack was and the kind Lyndon is."

"When something really crisis happens, that's when they're going to miss Jack. And I just want them to know it's because they don't have that kind of president and not because it was inevitable."

Jacqueline Kennedy was also dismissive of Johnson's wife, Lady Bird Johnson. She recalled that Lady Bird Johnson would follow her husband around and make notes about his conversations with others, "sort of like a trained hunting dog."

"She had every name, phone number – it was a – ewww – sort of a funny kind of way of operating."

The interviews occurred during a tenuous time in the relationship between Jacqueline Kennedy and President Johnson, historian Michael Beschloss, who wrote the book's introduction and footnotes, told ABC News.

"LBJ made a very big effort to make sure that Jacqueline Kennedy was on the reservation from his point of view, and on these tapes he keeps on calling her up and saying come down to the White House. And she says I can't bear to do it, it'll make me start crying again," Beschloss said. "Johnson had nightmares that he would get to the Democratic Convention in 1964, and in would come Bobby Kennedy and Jackie Kennedy -- stampede the delegates to vote for not LBJ but RFK for president."

Johnson would win renomination in 1964, although his rivalry with Robert Kennedy would continue. Robert Kennedy left his post as Johnson's attorney general in September 1964, and later broke publicly with Johnson on Vietnam.

Robert Kennedy's decision to seek the Democratic nomination in 1968 helped push Johnson out of that race. Robert Kennedy was assassinated in June 1968.

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