But a formidable array of critics have challenged Caro’s portrait of LBJ. Means of Ascent, which deals almost entirely with the 1948 election, was engulfed by criticism when it was published in 1990. “By tilting the tables to make crystal-clear the personal abhorrence he has come to feel for his subject,” David Broder wrote, “[Caro] strains credulity.” “Though Caro likes to present himself as a simple fact collector on a giant scale,” Garry Wills thundered, “he is actually a mythmaker, and what he gives us in this book is a nightmarishly inverted fairy tale.’

Now Caro faces a dual challenge: to please both his critics and his publisher, Knopf, which is printing 200,000 copies of a book about Lyndon Johnson’s twelve-year tenure in the U.S. Senate.

“You’re really happy to be done; Caro remarks with a chuckle one recent afternoon. His desk is nearly empty, except for some white legal pads, the galleys for Master of the Senate, and a Smith Corona Electra 210, the model on which he composed The Power Broker. (He bought seventeen Electra 210s when the company quit making them decades ago.) The typewriter looks small and vulnerable on his massive desk. Caro’s relief is reflected in his attire. Normally he arrives at his Fifty-Seventh Street office dressed in a jacket and tie, but today, his book finished, he is wearing a dark blue sweater, a light blue shirt, and gray trousers. With his preppy appearance and tortoise-shell glasses, he looks like the Princeton man that he is. The phone hums. The caller is Walter Isaacson, chairman and CEO of CNN News Group, expressing his enthusiasm for the New Yorker’s second excerpt from Master of the Senate, which just hit the streets.

“I’ve never been interested in writing a book just to show the life of a famous man,” Caro explains. “Each book is about something else. It’s the life of Lyndon Johnson that’s holding it together, but the books are really about political power.” Master of the Senate took some nine years to write. Caro has been working on Johnson for a quarter-century, and he still hasn’t arrived at Johnson’s presidency: the new book ends in 1961.

To immerse himself in the Senate, Caro moved to Washington, where he sat in the Senate Gallery (for which he received a special pass); he haunted the cloakrooms; and he kibitzed with Senate staff. Caro also conducted a thousand interviews, perused (along with his wife) nearly three hundred oral history transcripts, and ran his eyes over many hundreds of thousands of documents. It was a herculean effort, and Senate staffers were impressed by it. “I don’t think anybody has tried to grapple with the institution, as much as Caro has, in half a century,” says Donald Ritchie of the Senate Historical Office.

Capturing other worlds is an endeavor to which Caro has dedicated his life. He spends much of his time on the road, plundering archives and conducting interviews all over the country, but much of his work, and all of the writing, is done here—on the twelfth floor of the Fisk Building in Manhattan. The building itself, a warren of suites filled with dentists, literary agents, and small-business people, imparts a shabby elegance. Caro’s immaculate office is twenty-two feet by twenty-two feet. One wall is filled with bookshelves and crammed file cabinets; another wall contains a massive cork board, which he plasters with detailed outlines of his chapters. There is a couch, on which he sometimes naps.

This is the office of a man who takes himself, and his work, seriously. It’s a monastic, claustrophobic space. There are no sources of music, no pieces of art. There are no photographs, except for a single image of the U.S. Senate chamber, emptied of its occupants, which hangs on the bulletin board. Only the big window provides relief. The austerity of the room is deliberate: “It’s too hard to write,” Caro says wearily. “It’s too easy not to write. If you could do anything else, you’d be doing it.” But write he does. Caro keeps track of his daily word count on a calendar. “Hemingway wrote the word count every day,” Caro avers. “So do I.” He also keeps a note attached to his desk lamp, a stark reminder of his priorities: “When you’re at this desk,” the note reads, “the only thing that matters is what is on the page.”

Scott Sherman is a contributing writer at The Nation and a contributing editor at the Columbia Journalism Review.