What did you think would be the Republican reaction to the latest revelations about Donald Trump? Did you expect the party’s luminaries to drop their collective head into their hands, or to crumple into a heap in despair at the state of the man they anointed as president of the United States?

They’d certainly have had good reason. In the book Fire and Fury, which on Thursday received the greatest possible endorsement – namely a “cease and desist” order from Trump’s personal lawyers – the journalist Michael Wolff paints a picture of a man whose own closest aides, friends and even family believe is congenitally unfit to be president.

The Trump depicted in the book is ignorant: the adviser who tried to teach him about the constitution could get no further than the fourth amendment before Trump’s eyes glazed over. He doesn’t read, or even skim, barely having the patience to take in a headline. Some allies try to persuade Wolff that attention deficit disorder is part of Trump’s populist genius: he is “post-literate – total television”.

The Republicans have predicted many times that Trump would change. They've been wrong every time. He won’t change

He is also loathsome: we read that a favourite sport of Trump’s was tricking friends’ wives to sleep with him. He is weird, especially in the bedroom: having clashed with his secret service bodyguard over his insistence that he be able to lock himself into his quarters (Melania has separate accommodation), he demanded the installation of two extra TV sets, so he could watch three cable news channels at once. He heads back under the covers as early as 6.30pm, munching a cheeseburger as he soaks up hours of Fox and CNN. If there are crumbs, the chambermaid can’t change the sheets: he insists that he strip the bed himself.

We learn that Trump believes Saturday Night Live is damaging to the nation and that it is “fake comedy”; that daughter Ivanka wants to be president herself and that privately she mocks her father’s nature-defying combover. And, perhaps most amusingly, we get an answer to the question that has long enraged Trump: the identity of the mystery leaker behind the stream of stories of White House chaos and fratricidal dysfunction that have appeared since he took office. It turns out that the president rants endlessly on the phone to his billionaire friends, who feel no duty of confidentiality. In other words, the leaker Trump seeks is … himself.

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

Given all this material, you’d forgive congressional Republicans for being glum. Alternatively, you’d understand if they tried to denounce the book, perhaps joining those who question Wolff’s methods, believing he too often strays from corroborated facts and cuts journalistic corners. But that has not been the reaction.

Facebook Twitter Pinterest Donald Trump with Steve Bannon during a swearing-in ceremony for senior staff in January 2017. Photograph: Carlos Barria/Reuters

Instead, the official campaign account for Mitch McConnell, the Republican leader in the Senate, tweeted a gif of McConnell grinning mightily. And that smirk captured the mood of many of his colleagues. What do they have to smile about? They’re pleased because they believe Fire and Fury marks the downfall of Steve Bannon, the former chief strategist to Trump and source of some of the book’s most scathing lines. It was Bannon who told Wolff that Trump had “lost it”, and Bannon who described the meeting Donald Trump Jr had with a Russian lawyer – convened for the express purpose of receiving dirt on Hillary Clinton – as “treasonous”.

Trump’s response came in the form of a long and furious statement that loosely translates into New Yorkese as “You’re dead to me” – which delighted establishment Republicans who have long seen Bannon as the enemy within.

It would be nice if this loathing were rooted in ideological principle, with Republicans despising Bannon as the apostle of an ultra-nationalist isolationism and xenophobia that could tip the US and the world towards a 1930s-style catastrophe. (Recall that Bannon once promised Wolff the Trump administration would be “as exciting as the 1930s”.)

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But the truth is that Bannon posed a threat to McConnell and his ilk, vowing to run insurgent, Trump-like candidates against establishment Republicans in primary contests (just as he did, in vain, in Alabama last year). If Bannon is broken, they can sleep more easily.

Some go further, believing that, as Bannon dies, so does Bannonism. They speculate that, with the ties to his onetime evil genius severed, Trump might now moderate, becoming a more conventional, focused occupant of the Oval Office. This is delusional, twice over.

First, it’s true that things look bad for Bannon now: he has apparently lost the financial backing of the billionaire Mercer family, and it’s possible he stands to lose control of his far-right Breitbart media empire. But he understands Trump and knows that, if you’re ready to grovel and flatter, a rapprochement is always possible. Hence Bannon’s declaration on Thursday that Trump is a “great man”.

But the more enduring delusion is that Trump is poised to moderate. Republicans predicted he would change once the primaries of 2016 were under way. Then they said he would change once he’d won the party nomination. Or when the presidential election campaign proper began. Or when he’d won the election. Or once he’d taken the oath of office. They were wrong every time. He won’t change. Trump is Trump.

The sheer persistence of this delusion points to another one: the hope that Republicans will finally decide enough is enough and do the right thing by ousting this unfit president. The Wolff book has prompted another flurry of that speculation, focused this time on the 25th amendment of the constitution, which allows for the removal of a president deemed “unable to discharge the powers and duties of his office”.

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In an article this week, Wolff provides arresting evidence of mental deterioration. He writes that Trump would tell the same three stories, word-for-word, inside 30 minutes, unaware he was repeating himself. “Now it was within 10 minutes.” He adds: “At Mar-a-Lago, just before the new year, a heavily made-up Trump failed to recognise a succession of old friends.” But the 25th amendment requires the agreement of the vice-president, a majority of the cabinet and, ultimately, both houses of Congress. We are, once again, up against the sobering truth of the US constitution: it is only as strong as those willing to enforce it. And, today, that means the Republican party.

These latest revelations prove – yet again – what a vile, narcissistic and dangerous man we have in the Oval Office, wielding, among other things, sole, unchecked authority over the world’s mightiest nuclear arsenal. But the reaction to them proves something else too. That he remains in place only thanks to the willing connivance of his Republican enablers. As culpable as he is, they share in his damnation.

• Jonathan Freedland is a Guardian columnist