Were I running a modestly sized whelk stall, let alone the White House, the very last person I would allow behind the scenes to observe and report on its secrets would be Michael Wolff.

Please understand: the author of Fire and Fury, the book that has rocked Donald Trump’s presidency, is a brilliant journalist. Having commissioned and edited his work in the past, I can vouch for his terrier-like pursuit of the truth and his diffident charm when handling his subjects.

That’s precisely why no remotely competent adviser would have given Wolff a backstage pass to the working life of a president who knew nothing about politics or policy, had expected (even wanted) to lose, and had no intention of reining in his blowhard, bullying persona. It says so much about the amateurism of the team around Trump that Wolff was allowed to be, in his own words, a “constant interloper”. The very existence of this book by this author tells a story in itself. It is a case of form perfectly matching content.

Of course, we are all beneficiaries of this spectacular failure to exercise due diligence. Do not be distracted by those who are scouring the book for minor errors. The big story is what matters, and Wolff has nailed it.

Play Video 1:18 Fire and Fury: Key explosive quotes from the new Trump book - video

For a start, he has scotched once and for all the nonsensical claim that we should take Trump seriously but not literally. The figure described in Wolff’s pages is indeed an arch fantasist, but also capable of more or less anything. He cannot comprehend that firing the FBI director James Comey will compound his problems (“He doesn’t necessarily see what’s coming,” was the laconic reaction of Steve Bannon, formerly his strategy director, now his mortal enemy). Trump talks often of sacking Robert Mueller, the special counsel investigating his connections with Russia.

The president’s staff struggle in vain to keep him from making wild threats against North Korea. On his Marine One helicopter, he tries to rationalise membership of the Ku Klux Klan. He is literal-minded in the manner of a toddler – with the difference that, as he warned Kim Jong-un in a tweet last week, he has a nuclear button.

The milieu described by Wolff more closely resembles the court of a crazed medieval monarch than a traditional West Wing. Access is all, faction is all, expertise is eclipsed by animus. Bannon, Reince Priebus (until last July his notional chief of staff), his son-in-law Jared Kushner, his daughter Ivanka, and others, vie with scant dignity for the role of gatekeeper and high chamberlain. Bannon calls Ivanka “a fucking liar” in front of her father – who only remarks: “I told you this is a tough town, baby.”

At times, Trump roars in the manner of the world’s stupidest King Lear, as Ivanka stumbles behind him, a clueless Cordelia. Bannon makes a fine Iago, alongside a rep company of useless aides rotating as Rosencrantz and Guildenstern.

The trouble is that the metaphor is not really a metaphor. Essentially, Trump has annexed the presidency to the world of show business, the starring role of a performance career that has stretched from the WWE ring via numerous film cameos to the Oval Office. He perceives the public as an audience consuming entertainment rather than a civically engaged electorate.

Not surprisingly, the book has turbo-charged the allegation that the president is experiencing psychiatric problems, or is suffering from a neurological disorder.

Donald J. Trump (@realDonaldTrump) ....Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart. Crooked Hillary Clinton also played these cards very hard and, as everyone knows, went down in flames. I went from VERY successful businessman, to top T.V. Star.....

This is sensitive terrain: there are few qualified clinicians in the political and media class, and none who have examined Trump professionally. Yet the president himself has made his psychiatric condition an issue by insisting – again, via Twitter – upon his “mental stability” and claiming to be “like, really smart” (a verbal formula that undermines the very point it is trying to make). It is fair to assume that a person who feels the need to claim he is “a very stable genius” is no such thing.

One is reminded of the (possibly apocryphal) story about an early campaign by Lyndon Johnson, who instructed his team to allege his opponent had a taste for bestiality. “We can’t get away with calling him a pig-fucker,” said his campaign manager. “Nobody’s going to believe a thing like that.” To which Johnson replied: “I know. But let’s make the son of a bitch deny it.” By denying he is mad, Trump has given the claim the widest possible circulation.

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Wolff has performed a significant democratic service by quashing definitively the always-ridiculous notion that Trump would be “normalised” by office.

But alas, I do not share the author’s confidence, expressed on the BBC’s Today programme, that “we will end this presidency now”. To remove a president from office, the House of Representatives must vote to send the case to the Senate – where the US constitution requires “the concurrence of two-thirds of the members present” for a conviction. The alternative route is the 25th amendment, which allows vice-president Michael Pence and the other 15 cabinet members to declare Trump “unable to discharge the powers and duties of his office”.

The constitutional means are there. But is the political will or the arithmetic? True, the 2018 mid-terms may change the balance of power in Congress. Bannon could be right that the Russia scandal is all about money laundering and will provide Mueller with a “path to fucking Trump”.

But, for now, there is little evidence of a taste for impeachment, or a readiness to put the interests of the republic first.

It is even less likely, at least at this stage, that Trump’s executive appointees, led by Pence, will depose him. The 25th amendment is only half a century old, and has never been invoked against the wishes of the incumbent president. Does anyone seriously believe that Trump, declared psychiatrically or neurologically incapacitated by his own cabinet, would shuffle meekly from office? Such a threat would trigger all his most brutal attributes: his belief that the establishment is against him and his proven ability to mobilise great swaths of the American electorate in a common hatred of Washington. Now, that really would be fire and fury.

Which leads to the most alarming contemplation of all: that, far from decaying into seething obsolescence, this president may just be getting started; and that Wolff’s book, for all the mania it reveals, might only describe the first, appalling stage of a journey into the wasteland.

• Matthew d’Ancona is a Guardian columnist