The Canadian Prime Minister, Justin Trudeau, was less than forty-eight hours away from hosting the biggest diplomatic gathering of his career when I spoke with one of his top advisers on Wednesday afternoon. Trudeau’s team was searching for strategies to salvage the annual G-7 summit with the American President, Donald Trump, and leaders of five of the world’s other large democratic economies—all of them close allies of the United States, and all of them furious with Trump. “Look, he personally decided he wanted to be fighting with everybody,” the Trudeau aide told me, referring to Trump. “Maybe he thinks it’s in his best interests to be combative and fighting.”

For close to a year and a half, Trudeau and his counterparts have employed various strategies to try to head off conflict with the volatile American President, from flattery to stonewalling to hours of schmoozing on the golf course. But in recent weeks Trump has confounded their efforts, unleashing a tit-for-tat trade war with allies, blowing up the Iran nuclear deal over European objections, and walking away from a deal with Canada and Mexico to overhaul NAFTA, all while lavishing praise on the North Korean dictator with whom he hopes to reach an accord next week. Adding insult to injury, Trump even cited an obscure national-security provision to justify the tariffs, as if America’s closest friends had suddenly become its biggest enemies. As a result, the G-7 meeting that Trudeau will host on Friday and Saturday was shaping up to be the most contentious, and possibly the most consequential, since the summits began, in 1975.

Trump’s chief economic adviser, Larry Kudlow, told the White House press corps on Wednesday that this was all just a “family quarrel,” but, if so, it’s one ugly fight. As Kudlow acknowledged the rift, Trudeau and France’s President, Emmanuel Macron, were meeting to plot strategy, and everyone was wondering why Trump, who is often described as averse to face-to-face conflict, had chosen the weeks preceding the annual G-7 summit to punch his allies in the face. In the days leading up to the meeting, Trump had tense phone calls with Trudeau, Britain’s Prime Minister, Theresa May, and Macron, who has been especially humiliated by the series of adverse decisions after flying to Washington to lobby Trump personally. All of them appear to fix blame on Trump himself. “We’ve gotten used to unorthodox behavior from your President,” the Trudeau adviser said.

For his part, Trump seems to relish the confrontation he has unleashed and is spoiling for more. On Thursday morning, the President tweeted that he was “getting ready to go to the G-7 in Canada to fight for our country on Trade,” insisting, as he often does, that “we have the worst trade deals ever made.” But others involved in the summit were preparing for an America more alone than ever before, and now Trump faces the very real risk of allies teaming up against him. “The American president may not mind being isolated, but neither do we mind signing a 6 country agreement if need be,” Macron tweeted pointedly to Trump, in English, later on Thursday. Trump quickly fired back. “Please tell Prime Minister Trudeau and President Macron that they are charging the U.S. massive tariffs and create non-monetary barriers,” the President tweeted. “Look forward to seeing them tomorrow.” Soon after that, the White House said in a statement that Trump would skip the second day of the summit entirely, and it seemed increasingly certain that the traditional joint communiqué signed off on by all seven leaders will be discarded because of Trump. (As of Wednesday, when it would normally be in the final stages of elaborate negotiations, the communiqué was not even being circulated.) Instead, the Trudeau adviser told me, the Canadian Prime Minister, as the summit’s host, was likely simply to release a “statement from the chair,” summarizing the discussions without requiring Trump to approve it. The American President has blundered his way into “opening a four-front-at-least war simultaneously,” the Trudeau adviser said, and now the goal of the summit has become unlike any other that preceded it: “to get allies together to try to contain the amount of damage he’s doing.”

Ever since Trump took office, America’s allies have desperately sought to avoid this moment. Over the last year and a half, though, many of them have come to realize, with growing dread, that it was inevitable. The rift between the world’s great democracies that Trump’s election portended is coming to pass, and it is about far more than Iran policy, obscure trade provisions, or whether Germany spends two per cent of its G.D.P. on NATO. Many senior European officials speak of it, as one Ambassador to Washington did to me recently, as nothing less than a “crisis of the West.”

As Trump’s dramatic moves have played out this spring and hardened into a Presidential narrative of American victimization at the hands of free-riding allies, senior government officials in London, Berlin, and other European capitals, and in Washington, have told me they now worry that Trump may be a greater immediate threat to the alliance than even authoritarian great-power rivals, such as Russia and China. Equally striking is the extent to which America’s long-term allies have no real strategy for coping with the challenges posed by such an American President. Trump may be reorienting U.S. foreign policy away from its closest friends, such as Great Britain and Germany, and toward those with whom Trump is more politically aligned in Israel, the Gulf, and along Europe’s restive fringes, but his traditional partners have no real strategy for how to respond.

Last year, the German Foreign Office embarked on what two sources described to me as its first-ever effort to produce an America strategy aimed at answering that question, with the goal of producing a strategy document similar to those it has for adversaries. “Essentially, it’s an overhaul of German foreign policy,” a senior German official told me, “since the key assumption being called into question is the total reliance we have on the friendship with the U.S.” Work on the new strategy began after Trump’s Inauguration but accelerated last spring, after the German Chancellor, Angela Merkel, returned from Trump’s initial foray into international summitry rattled by him and announced that “Europeans must really take our fate into our own hands.” The painful realization, the senior German official said, was that “we might get to a situation where we see Americans not only as friends and partners but also as competitors and adversaries. We don’t want to do that. That is how we treat other great powers around the globe, like Russia and China.”

Until now, allies have been notably divided on how to handle Trump, largely settling on an approach that Charles Kupchan, who served as President Barack Obama’s senior director for Europe at the National Security Council, characterized as “limit the damage and run out the clock.” Trump’s recent confrontational moves, however, have made it all but impossible for allies to continue with their policy of “don’t give in but don’t give up,” as Kupchan described it. In interviews in Europe and Washington over the last week, I heard a new tone of anguish and concern as the extent and consequences of the rift have become more clear. “They cruised through 2017 and they thought everything was fine,” Julianne Smith, a former Pentagon official and deputy national-security adviser for Vice-President Joe Biden who now heads the transatlantic program at the Center for a New American Security, told me. “Now he is doing in 2018 what he threatened to do, and it’s ‘Oh, no, I feel the shock and awe’ and ‘What can we do?’ ”