In May 1964, just months after John F. Kennedy’s assassination, President Lyndon Baines Johnson had to decide whether to run for reelection. With pressure picking up to escalate the Vietnam War, and civil-rights legislation stuck in Congress, he doubted he would be able to unify the country. He asked his most trusted political adviser to set out the pros and cons of seeking the presidency in his own right.

The nine-page memo he received in response was both convincingly constructed and startlingly prescient. It opened with a draft announcement of a decision not to run, shrewdly forcing Johnson to confront how such a move would feel. But after acknowledging that he could choose to leave the White House, it also laid out a projected timeline of the continued Johnson presidency, concluding with the correct prediction that he would “announce in Feb. or Mar., 1968 that you are not a candidate for re-election.”

The most significant thing about the memo, though, was its author. I came across the document in a folder at the LBJ Library called “Campaign Letters, Lady Bird Johnson to Lyndon Johnson.” When she wrote it, the vice presidency was vacant—LBJ had yet to name Hubert Humphrey to the job—and the traveling press corps used to refer to Lady Bird only half-jokingly as “Mrs. Vice President.” She even wrote notes to LBJ, feedback on his speeches, for example, on White House stationery printed with office of the vice president.

CTJ, the initials she used for her full name, Claudia Taylor Johnson, was a woman who knew her place in history and left sufficient evidence to suggest that she wanted us to know it too. Yet in most historical accounts of her role in LBJ’s presidency, she is depicted as a loyal, cuckolded wife who focused on the frivolity of beautifying America at a time of transformative social and political change.

But she also left us her own account, an audio diary of her five-plus years in the White House—123 hours of tape filled with 1,750,000 words in an entrancing East Texas drawl. She recorded the first entry just eight days after the JFK assassination, before the Johnsons had even moved into the White House. She made her final entry on the last day of January 1969; by then, the couple had returned to the LBJ Ranch in Texas.

Her complete, unedited recordings, first hinted at in the highly redacted book A White House Diary, published in 1970, reveal her central role in shaping some of the most consequential decisions of LBJ’s White House years. The audio offers a crucial record of her dedication to civil rights and the Great Society, her pioneering work in environmentalism, and her riveting accounts of three political assassinations. It shows her clarity and her blind spots (especially over Vietnam), her deft use of language and imagery, her judgment of character, and her 360-degree command of detail. The result is a chronicle not just of a first lady’s day-to-day life, but of the entire Johnson presidency. And yet, despite all of that, for decades she has largely been relegated to caricature or all but overlooked in the innumerable biographies, political studies, psychohistories, reports, and analyses of her husband and his administration.