It’s war. The summit that was meant to celebrate Nato’s 70th anniversary as one of the greatest peacetime alliances in history ended in open hostility. Had it gone on for another day, nukes might have been fired. Donald Trump stomped off from the golf resort just outside Watford in a huff, cancelling his scheduled press conference. For the first time in living memory, the US president was lost for words – even the usual ones that mixed lies with unintelligibility.

There again, the writing had rather been on the wall long before the summit had even started. Having previously slagged off Nato at every opportunity, Trump had now become outraged that other countries were taking the US for granted and not paying their fair share. Emmanuel Macron had declared the organisation brain dead. President Erdoğan had started buying arms off the Russians.

Boris Johnson just wanted to avoid being seen in the same room as the US president during an election campaign. British voters might be happy to turn a blind eye to the prime minister’s liaisons with Jennifer Arcuri and others, but they took a dim view of his shameless brown-nosing to the Orange Sun Bed God.

Still, they all might have got away with it had the Canadian prime minister, Justin Trudeau, not been caught on camera sharing a joke about Trump’s chaotic press conference, with Johnson, Macron and Princess Anne at a Buckingham Palace reception.

Play Video Princess Anne, Johnson, Trudeau and Macron appear to joke about Trump at Nato summit – video

That stung Trump. The president might have few social skills – when he and Boris get together it’s a meeting of true narcissistic mindlessness – but even he can tell when he’s getting badly mugged off. So he had made a point of being the last to arrive for the Wednesday golf course meeting and keeping Boris waiting out in the cold. It was the least he could do to try to retrieve what passed for his self worth.

But having sulked through much of the three-hour summit meeting, Trump couldn’t contain himself during a bilateral meeting with Angela Merkel. Trudeau was two-faced, he declared. Thereby undoing 70 years of Nato diplomacy in one sentence. The Canadian prime minister was just sore that he had been called out bigly – the bigliest even – for contributing less than the agreed 2% on the Nato budget.

Merkel wisely kept her head down. Now was probably not the best time to tell the president that all the other 28 Nato leaders laughed at him behind his back. This wasn’t about the 2%. It was about the president being a total joke. A dangerous joke admittedly, but a joke nonetheless. Meanwhile Trump looked momentarily thrilled to have once again captured the media’s attention – even if he wasn’t entirely sure why – and riffed for a couple of minutes on how terrible the Canadians were, before cancelling his own press conference. He’d probably said too much already. Besides, it was time to get out of this god-forsaken hell hole.

At his own press conference, Johnson had tried to play the complete innocent. He couldn’t imagine how anyone might have imagined he had been laughing at President Trump. So it was left to Trudeau to tidy things up. It turned out that for once Trump had been fairly accurate in his assessment, as the Canadian went full two-faced. Sure they had all been having a laugh. But with the president not at him. He loved the orange panda to bits. The guy was the life and soul and all the other world leaders really looked up to him. His tie! His intelligence! His insight! Hell, the Donald had it all. And he just couldn’t wait till the next G7 at Camp David.

On the way back home, Johnson breathed a sigh of relief. The summit had been a disaster, but his kind of disaster. He hadn’t even dared hope the president would cancel his presser. So much possible shit averted. Everyone would talk of the Trump-Trudeau spat and no one would mention the NHS. The west might be one step nearer to being at war with itself. But Boris was one step nearer winning the election.

John Crace’s new book, Decline and Fail: Read in Case of Political Apocalypse, is published by Guardian Faber. To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min. p&p of £1.99.