The latest on Donald Trump’s state visit, now reportedly reinvented as one of those new, 3G, multigenerational vacations, and featuring an all-inclusive “togethering” trip to the world’s oldest theme park, mentions presidential hopes for a meeting between his daughter, Ivanka, the former model, and William and Kate.

As nightmarish as it sounds, Ivanka’s outreach could be the Trumpian idea of diplomacy, not least because Ivanka, recently returned from Africa, now has her own adventures in white saviourship to share. Any protracted Donald-Kate encounter has looked unlikely since 2012, when he commented on illicitly taken photographs of the duchess sunbathing, topless. The royal couple, who later won £92,000 in damages, said: “The incident is reminiscent of the worst excesses of the press and paparazzi during the life of Diana, Princess of Wales.”

Trump studied the snaps. His opening tweet, posted at 7.03pm, around the time at which – we now know – he likes to retire to his bed with junk food, read: “Kate Middleton is great – but she shouldn’t be sunbathing in the nude – only herself to blame.” After a minute’s consideration, he added: “Who wouldn’t take Kate’s picture and make lots of money if she does the nude sunbathing thing. Come on Kate!” Still disapproving, he phoned Fox & Friends: “Why would she be outside in the nude? Why would she be standing in the nude in a swimming pool…?”

In the absence of a formal apology, the palace is presumably enacting hallowed banqueting conventions for seating a visiting president and a local princess he has victim-blamed. A minimum of 15 place settings always, since Victoria’s time, separates a foreign head of state from anyone – above the rank of duchess – he has slutshamed, more if the visitor’s recent past also features, as with this president, leering, sulking, tantrums, handshake fights and the verbal abuse of women. In fact it’s amid the rigours of correct perv- or villain-placement that the palace’s vast, internationally unrivalled collection of superannuated or otherwise ostensibly useless minor royals really comes into its own. Princess Michaels of Kent are like teaspoons: you can never have too many of them. As for Andrew, fellow full-time golfer and frequent flier with an uninhibited hatred of the press, he is predicted to be worth his weight in gold throughout the Trump visit.

In the circumstances, a Kate and Ivanka encounter would offer a fresh start; a chance for the younger generation to bond over shared experience: Trump is famous for being sinister about his own daughter too! Asked if Ivanka might pose in Playboy, he said: “She does have a very nice figure. I’ve said that if Ivanka weren’t my daughter, perhaps I’d be dating her.”

‘In the circumstances, a Kate and Ivanka encounter offers a fresh start.’ Photograph: Mike Blake/Reuters

With William present, Ivanka also has a chance to dispel any lingering awkwardness relating to Trump’s sexual interest in his late mother, to the point that Diana apparently felt she was being stalked. Subsequently, as well as agreeing in public that he could have “nailed” Diana (providing she’d passed an HIV test), Trump wrote, in The Art of the Comeback: “I only have one regret in the women department, that I never had the opportunity to court Lady Diana Spencer.”

In her history of state visits, this is probably the first time, then, that the Queen finds herself entertaining a head of state who is not merely obnoxious, mendacious, unprincipled, vain, racist, sexually predatory, misogynistic, loutish, untrustworthy, a threat to world peace and, given his denial of the climate emergency, also to future generations, but who has also indicated a creepy interest in two female members of her own family. Perhaps, though, when your job description has included hospitality for certified murderers, that hardly signifies. And it’s not as if Trump’s had any of her citizens assassinated with polonium or novichok, like one unreformed house guest. The one who is also close to Trump and Trump Jr.

Even at the age of 93, and with massive street protests in prospect, the Queen might feel that the royal escort work that has seen her endorse Ceausescu, Mugabe and any number of bloodstained patriarchs is something she cannot reasonably withhold from the strong and stable genius now fomenting war with Iran.

But Charles, new to the job, could review this recently invented tradition; leave the obvious contamination risk with the Foreign Office. He doesn’t need to welcome Trump, and attend his banquet, and award the brand the further favour of a private cuppa. But these priceless PR gifts to a man who thought it worth faking a Time magazine cover (“Trump is hitting on all fronts!”), along with the symbolic recognition for a fellow dynasty, have been welcomed as evidence of maturity on the part of the occasionally mutinous prince.

So empty claims about the national benefits that flow from staging military parades and parties for psychopaths will not, you gather, cease with his mother’s reign. Under King Charles III, too, we will continue to appreciate the fatal – if unidentified – consequences for British prosperity were visiting royals and rogues ever denied the chance to discuss travel arrangements with below-the-radar diplomats Beatrice and Eugenie.

Whether the prince plans to explain sustainability to Trump, or has come to believe, like the Queen, that it’s a sovereign’s sacred destiny to be pimped out, his warm welcome for the pussy grabber takes little account of possible public feeling about the value and decency of these rituals, even when the visitors are not flagrantly disgusting. Since the only obvious beneficiaries of ceremonial visits are their star performers, the prince’s role in the upcoming show also casts light on his commitment to averting catastrophic climate change.

Trump’s visit is designed to enhance the status of the world’s leading climate crisis denier. It will advertise, simultaneously, the dutiful contributions of his royal hosts. Charles must have decided that the end justifies the means.

• Catherine Bennett is an Observer columnist