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French President Emmanuel Macron and his wife Brigitte Macron welcome Canada's Prime Minister Justin Trudeau at the G7 summit in Biarritz, France.

CHRISTIAN HARTMANN/Reuters

The Group of Seven summit in Biarritz, France, is underway and faces its ultimate stress test. Donald Trump blew up the last two G7s, going so far as to insult the host of 2018’s Canadian edition – he called Justin Trudeau “dishonest and weak” – and may be equally dismissive of the event and its leaders this time around.

A hat-trick of failures might not kill off the G7 summits, but could render them effectively irrelevant. This year’s host, French president Emmanuel Macron, has already set the “success” bar exceedingly low. He is doing away with the final communique, knowing full well that the chances of consensus on any issue, from tariffs to the environment, are low even though he has a couple of allies, notably Mr. Trudeau. His biggest fear is a repeat of the Canadian G7 fiasco. Robbing the media of an easy target – the communique, or lack thereof – was a clever though cynical move.

Mr. Macron is not alone in preparing for the worst. On Saturday, European Council president Donald Tusk made it amply clear that Europe and America were divided on many fronts. “This is another G7 summit which will be a difficult test of unity and solidarity of the free world and its leaders,” he told the media. “The last years have shown that it is increasingly difficult for all of us to find common language when the world needs our co-operation more, not less.”

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Mr. Trump is the biggest obstacle to the G7’s credibility. CNN reported that he was wondering whether he should even show up at Biarritz. He’s going, probably because he is hosting 2020’s G7 (no doubt at one of his golf courses), knowing that a no-show in Biarritz might trigger a boycott next year among some G7 leaders. He will want his own G7 platform to boast about the wonders of the U.S. economy as his re-election campaign hits full stride. That is, assuming America is not mired in recession by then.

Mr. Trump comes to Biarritz in a combative mood. The trade war with China is intensifying by the week, with both countries in the last few days announcing new tariffs on top of old tariffs; investors reacted by sending the markets yet another step closer to the cliff edge. Europe – four of the G7 countries are European – is in a near panic that the tariff war unleashed by Mr. Trump will sink their economies. Germany and Italy, the two European economies most reliant on exports, are already flirting with recession. But Europe’s health seems of no concern to Mr. Trump; China is his target and Europe is merely collateral damage.

There’s more, lots more. Brexit is coming at the end of October whether or not Britain has an exit deal with the European Union, insists Britain’s new (and unelected) prime minister, Boris Johnson. Mr. Trump supports Brexit and is making nice with Mr. Johnson, much to the alarm of the G7’s European members, and also to Japan, which built car factories in Britain on the assumption that EU and its frictionless trade status would remain intact.

Mr. Trump has attacked Mr. Macron’s promise to launch a 3 per cent digital revenue tax, which is designed to ensure that the American tech giants actually pay tax in the countries in which they operate instead of shunting profits into tax havens like Ireland and Luxemboug. Mr. Trump has vowed to hit French wines with 100 per cent tariffs in retaliation (never mind that Mr. Trump’s own Treasury secretary, Steve Mnuchin, has agreed in principle that tech companies should be taxed where they make their money). Mr. Trump also plans to restore the G8 by inviting Russia back into fold. Russia was expelled from the G8 in 2014 after it seized Crimea. Mr. Macron said Russia’s unconditional readmission is a non-starter.

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And so on. But Mr. Trump is not the G7’s only bruising factor. The G7’s European members might find it impossible to present a united front against Mr. Trump. Mr. Johnson is desperate for a post-Brexit trade deal with the United States, as he is with the EU. It’s in his best interests to play kissy-kissy with the G7 members on both sides of the Atlantic. Italy has become an unreliable EU ally. Its government collapsed last week and new elections seem certain. The deputy prime minister and effective leader of Italy, Matteo Salvini, is a Euroskeptic and an admirer of Mr. Trump’s anti-migrant policies.

Even Germany and France come into the summit at odds on several issues. One is the destruction of the fire-ravaged Amazon. Mr. Macron has said he would block a trade deal with South America’s biggest economies, dominated by Brazil, unless Brazilian president Jair Bolsonaro takes environmental protection seriously. But German chancellor Angela Merkel doesn’t think that killing the trade deal will encourage Mr. Bolsonaro to douse the Amazon fires; she fears it could have the opposite effect.

Mr. Macron needs allies to salvage the G7 summit from either destruction or irrelevancy. His closest ally appears to be Mr. Trudeau, who, like Mr. Macron, is building himself up as the champion of the liberal order in all its machinations, from free trade to practical approach to immigration.

Mr. Macron sees Mr. Trudeau as a progressive counter to the dark Trumpian forces. Canadian diplomats said that Mr. Macron was happy to hold the G7 summit in August, instead of September, to make life easier for Mr. Trudeau, who will almost certainly be in campaign mode next month on Canadian soil.

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Mr. Macron and Mr. Trudeau will bolster one another at the G7. They will be eloquent about the need to keep to the liberal order intact and to prevent the world’s largest economies from putting up walls. But Mr. Trump, as always, will be the big, unruly beast in the room. France and Canada alone will not be enough to spare this G7 from train-wreck status.

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