Wolff addresses the inherent challenge of reporting on this White House in an introductory author’s note, explaining that the recollections of sources can collide with one another and in some cases be untrue entirely. “Those conflicts, and that looseness with the truth, if not with reality itself, are an elemental thread of the book,” he says. To confront his problem, Wolff notes that there are times he lets “the players offer their versions, in turn allowing the reader to judge them.” Unfortunately for the reader, he throws up his hands when dealing with three of the most pivotal moments of the Trump campaign and presidency.

Image Ivanka Trump with her husband Jared Kushner and Gary D. Cohn, chief economic advisor, left, in the Rose Garden last April. Credit... Doug Mills/The New York Times

In recounting the 2016 gathering at Trump Tower among Donald Trump Jr., the campaign chairman Paul Manafort and Jared Kushner, the president’s son-in-law and close adviser, and a group of Russians promising damaging information on Hillary Clinton, Wolff offers several “why-and-how theories of this imbecilic meeting.” But he does not settle on any one of them.

Second, in recalling the moment on Air Force One a year later when now-President Trump worked to produce a statement for his son minimizing the meeting, Wolff does not attempt to assess the veracity of the declarations of Kushner and his wife, Ivanka, that they were not part of any cover-up. “Ivanka, according to the later recollection of her team, would shortly leave the meeting, take a pill and go to sleep,” Wolff writes. “Jared, in the telling of his team, might have been there, but he was ‘not taking a pencil to anything.’”

Wolff turns to the same device, only from the voice of the opposing camp, in recounting Trump’s fateful decision to fire the F.B.I. director James Comey. “It was Jared, in the version told by those outside the Jarvanka circle, that pushed for action,” he writes. (“Jarvanka” is Wolff’s shorthand, borrowed from Bannon, for Jared and Ivanka.) Wolff’s caution may be explained in his acknowledgments, where he gives a glowing tribute to his trusted libel lawyer. It is that sort of book.

Wolff is unsparing in his portrayal of Trump as an aberrant chief executive, not only detached from governance but barely literate. He summons withering on-the-record assessments from ostensible allies of a seemingly infantile president. “If they tell him the whales need to be saved, he’s basically for it,” says Katie Walsh, a former White House deputy chief of staff, recalling how easily the Kushners could sway Trump. Yet much of Wolff’s sourcing is opaque. “I’ve made stuff up forever, and they always print it,” Trump boasts about his long-running media con. But Wolff, with seemingly unintended irony, does not make clear where he harvested such an explosive line.