Lady Bird, we hardly knew ye.

We knew Claudia Alta Taylor Johnson as the long-suffering wife of the 36th president, the graceful presence in a White House led by a man of force and fury, the advocate of highway beautification, the curator of wildflowers. But we did not know her as a shrewd political analyst, a canny strategist, the sharp eyes of an administration that, for all its farsightedness on poverty and race, was blind to protest and shortsighted about Cold War strife.

Now we do. We do because Random House just published “Lady Bird Johnson: Hiding in Plain Sight,” Julia E. Sweig’s groundbreaking look at the 1,750,000 words in Mrs. Johnson’s diary of the 1,886 days of her husband’s presidency. In those pages, Sweig provides a guided tour of the passage of one of America’s most remarkable first ladies at a time of generational conflict and racial reckoning much like our own.

We heard tentatively and carefully from Mrs. Johnson when her “A White House Diary” was published in 1970, but it obscured more than it revealed. Two decades later, Harry J. Middleton, a Johnson speechwriter and later the director of the Johnson Library and Museum, published a Lady Bird biography carrying the subtitle “A Life Well Lived,” which was published by the Johnson Foundation and was more celebration than examination. In a lengthy interview Middleton arranged for me with Mrs. Johnson a quarter-century ago, she was generous — but hesitant and guarded.

She was neither hesitant nor guarded in her diary, and Sweig tells us that she views Mrs. Johnson as a “prodigiously disciplined participant, actor, and witness to and student of history,” adding: “Hidden within the sheer scale and, at times, overwhelming detail of the diary are golden nuggets of insight about her husband and herself, the marriage they created, and the ambitions animating the presidency they together crafted.”

This was how the Johnson presidency began, in a hushed, crowded hospital hall before the fevered rush to Love Field, an awkward swearing-in and a desperate flight back to Andrews Air Force Base:

Suddenly I found myself face to face with Jackie in a small hall. I think it was right outside the operating room. You always think of her, or somebody like her, as being insulated, protected. She was quite alone. I don’t think I ever saw anybody so much alone in my life.

In a way, that solitude in a crowd — “so much alone” — would be replicated by Jacqueline Kennedy’s successor. She also would know the deep responsibilities, the profound loneliness of White House life, and her life in the executive mansion would be dominated by the chants of protesters and the echoes of riots.

There was heartbreak from the first moment in the aircraft that had taken one president to Dallas and returned another to Washington:

The casket was in the hall. I went in the small private room to see Mrs. Kennedy, and though it was a very hard thing to do, she made it as easy as possible … Mrs. Kennedy’s dress was stained with blood. One leg was almost entirely covered with it and her right glove was caked, it was caked with blood — her husband’s blood. Somehow that was one of the most poignant sights — exquisitely dressed, and caked in blood.

But that also was the moment when, as Sweig put it, Mrs. Johnson “retired her from her fate as ‘a diminished supporting actor in the sweeping narrative dominated by her husband.'”

Mrs. Johnson was no shrinking wallflower, even in her embrace of wildflowers. Years earlier, a (male) reporter asked her to remark on Mrs. Kennedy’s hairstyle. “I think it’s more important what’s inside the head,” she said, “than what’s outside.”

Throughout the Sweig volume, we discover small insights that escaped the naked eye at the time.

Such as how Mrs. Kennedy helped Mrs. Johnson decide how the rooms in the private quarters of the White House should be occupied, with Lynda Johnson taking over Caroline Kennedy’s room and Luci Johnson moving into John F. Kennedy Jr.’s room. How Mrs. Johnson was far more understanding of Robert F. Kennedy, the slain president’s brother and LBJ nemesis, than was her husband. How the Johnsons, like the Eisenhowers, sometimes had supper on TV trays. (The Johnsons consumed shrimp curry rather than the Salisbury steak preferred by Ike and Mamie.)

And how Mrs. Johnson was preoccupied with the worry that the burdens of the presidency were killing her husband, and with the accompanying worry that the two of them were not doing enough, or fighting hard enough:

I have a growing feeling of Prometheus bound, just as though we were lying there on the rock, exposed to the vultures. … I had the feeling of wasted opportunities, of standing still when I should be running.

That is the result of a recurring theme inside the Johnson White House — and the Johnson marriage: How long should LBJ remain president? Should he run for office 11 months after the Kennedy assassination? Should — amid racial hostility, a stalemated war and metastasizing dissent over both — he seek another term in 1968?

To the tape recorder, she tried out her approach to her husband in 1964, walking through what it would be like to walk away:

That may be relaxing — for a while. I think it is not enough for you at 56. And I dread seeing you semi-idle, frustrated looking back at what you left.

Those White House years were a mix of achievement and torment. Listen in as Mrs. Johnson reflects the energy and exhaustion of those years:

I have been swimming upstream against the feeling of depression and relative inertia. I flinch from activity and involvement, and yet I rust without it. Lyndon too lives in a cloud of troubles, with few rays of light.

And later this:

For an extraordinarily healthy, tough, reasonably happy person, sleeping is becoming the hardest thing for me to do, particularly when I feel that I have not played my role well, that I have been a hindrance, not a help.

Some first ladies have historical significance because of their frailty (Mary Todd Lincoln, Ida McKinley), some because of their husbands’ frailty (Edith Wilson, Eleanor Roosevelt). Some had huge policy implications (Betty Ford, Hillary Clinton). But Lady Bird Johnson is perhaps alone, for she was significant for all those reasons.

David M. Shribman is the former executive editor of the Pittsburgh Post-Gazette. Follow him on Twitter at ShribmanPG.