Caro’s obsession with power explains a great deal about the nature of his work. For one thing, it accounts in large part for the size and scope of all his books, which Caro thinks of not as conventional biographies but as studies in the working of political power and how it affects both those who have it and those who don’t. Power, or Caro’s understanding of it, also underlies his conception of character and structure. In “The Power Broker,” it’s a drug that an insatiable Moses comes to require in larger and larger doses until it transforms him from an idealist into a monster devoid of human feeling, tearing down neighborhoods, flinging out roadways and plopping down bridges just for their own sake. Running through the Johnson books are what Caro calls “two threads, bright and dark”: the first is his naked, ruthless hunger for power — “power not to improve the lives of others, but to manipulate and dominate them, to bend them to his will” — and the other is the often compassionate use he made of that power. If Caro’s Moses is an operatic character — a city-transforming Faust — his Johnson is a Shakespearean one: Richard III, Lear, Iago and Cassio all rolled into one. You practically feel Caro’s gorge rise when he describes how awful Johnson was in college, wheeling and dealing, blackmailing fellow students and sucking up to the faculty, or when he describes the vicious negative campaign Johnson waged against Coke Stevenson. But then a volume later, describing Johnson’s championing of civil rights legislation, he seems to warm to his subject all over again.

In many ways, Caro’s notion of character is a romantic, idealistic one, and what fuels the books is disappointment and righteousness, almost like that of a lover betrayed. If there’s a downside to his method, it’s that anyone’s life, even yours or mine, described in Caro-esque detail, could take on epic, romantic proportions. The difference is that our lives would be epics of what it’s like not to have power, but the language would probably be the same. Caro has a bold, grand style — sometimes grandiose, his critics would say. It owes something to old-fashioned historians like Gibbon and Macaulay, even to Homer and Milton, and something to hard-hitting newspaperese. He loves epic catalogs (at the beginning of “The Power Broker” there is a long list of expressways that would not be out of place in the “Iliad” if only the Greeks and Trojans knew how to drive) and long, rolling periodic sentences, sometimes followed by emphatic, one-sentence paragraphs. He is not averse to repeating a theme or an image for dramatic effect.

This is not a style ideally suited to the chaste, narrow paragraphs of The New Yorker, especially in 1974, when it serialized “The Power Broker” in four installments that were long even then, when the magazine was so flush with ads it sometimes had trouble filling all its columns. I was a proofreader at The New Yorker then, and my office was across from that of William Whitworth, the editor of the “Power Broker” excerpts. I remember him wearily shuttling back and forth, like some Balkan diplomat, between the office of William Shawn, the magazine’s editor in chief, and one that Caro was borrowing while its occupant, Howard Moss, the poetry editor, was away for the summer. Caro complained that the magazine had tampered with his prose, and he wasn’t wrong. Instead of merely lifting some excerpts from the book manuscript, as was usually done, Whitworth tried to condense the whole thing, and this entailed squeezing out great chunks of writing, running the beginning of one paragraph into the end of another, pages away. “They softened my style,” Caro says. Shawn, on the other hand, had the magazine’s standards to uphold: The New Yorker insisted on its own, sometimes fussy way of punctuating; it didn’t approve of passages that were too leggy and indirect; it didn’t approve of repetitions; and it especially didn’t approve of one-­sentence paragraphs. A description of the situation in vigorous Caro-ese might read something like this:

“In the editorial world, William Shawn was a man of immense power. He wielded it quietly, softly, almost in a whisper, but he wielded it nonetheless. Not for nothing did some of his staff members privately call him the Iron Mouse. For writers, Shawn’s long wooden desk was like a shrine, an altar, and in the passing of proofs across that brightly polished surface — pages and pages of proofs, stacks of proofs, sheaves and bundles of proofs, proofs from the fact-checkers, the lawyers, the grammarians, proofs marked with feathery hen-scratch and with bold red-pencilings — they discerned something like magic, the alchemy that renders ordinary, sublunary prose free of impurity and infuses it with an ineffable, entrancing glow, the sheen of true New Yorker style.

“But that style was not for everyone.

“It was not for Robert Caro.”

The negotiations became so fraught that between the second and third installments there was a weeklong gap, unthinkable in those days, while the two sides stared each other down and it seemed that the next two parts might be scuttled. Everyone at the magazine was aghast. Caro, it turned out, was as stubborn as Shawn. Here was a 38-year-old unknown who hadn’t published a word except in newspapers. Moreover, he was broke, hardly in a position to turn his back on the biggest payday of his life so far, but alone among New Yorker contributors at the time, he dared to become a Bartleby and turn his powerlessness into a point of principle.

Caro now says that Shawn agreed to restore all the changes he cared most deeply about, but the magazine version nevertheless differs from the original and changes Caro’s punctuation and paragraphing. The New Yorker series is a very readable redaction of the original — and without sacrificing much essential information, easier on the attention span than the book, which requires an immense time commitment — but for better or worse, it’s not as full-throated as the original.

Whitworth, undaunted, excerpted the first volume of the Johnson biography in The Atlantic after he became editor there in 1980.

It’s not writing that takes Caro so long but, rather, rewriting. In college he was such a quick and facile writer, and so speedy a typist, that one of his teachers, the critic R. P. Blackmur, once told him that he would never achieve anything until he learned to “stop thinking with his fingers,” and Caro actually tries to slow himself down these days. He doesn’t start typing — on an old Smith Corona Electra 210, not a computer — until he has finished four or five handwritten drafts. And then he rewrites the typescript. When I visited him one day in early December, he was correcting the page proofs of “The Passage of Power” the way Proust used to correct proofs: scratching out, writing in between the lines, pasting in additional sheets of inserts.