Francois Mori / Reuters

PARIS—The ceremony was planned long in advance. A chance for French President Emmanuel Macron to welcome world leaders to mark the centenary of the armistice that ended the hostilities of World War I. A way to decry nationalism and reinforce his deep commitment to multilateralism, and to a European Union born out of past conflicts.

Then President Donald Trump came to town.

Since his arrival late Friday night, Trump’s every action has seemed emblematic of the unilateralism he has made the hallmark of his administration. And of the whiplash he tends to inflict on his hosts. First, Trump tweeted a direct attack on Macron, who has been calling for Europe to step up its own defense. The two men acted as if they had made up Saturday morning when they appeared—both manspreading in their chair with a forced smile—making brief remarks at the Élysée Palace before a bilateral meeting. Trump said he wanted a strong Europe. But it was clear the romance was over.

Then came the news that Trump would skip a central event of his 48-hour trip: a visit to the Aisne-Marne American Cemetery and Memorial outside of Paris, where he had been expected to honor American soldiers who had died in World War I. The White House said inclement weather prevented his helicopter from flying. But the site is an hour’s drive from Paris, and the weather wasn’t that bad. What was Trump doing instead? Whom was he meeting with? No details have yet emerged.

The vanishing act was classic Trump—dominating the news cycle, insulting and upstaging his hosts, to say nothing of U.S. soldiers and veterans. In the United States, Twitter blew up with anger at the president, and there was much chatter about how conservative media would have responded if a Democratic president had skipped a war commemoration because of a little rain. But here in Europe, Trump’s political theater underscored exactly what Macron, German Chancellor Angela Merkel, and other European leaders are increasingly concerned about: Europe is being isolated, if not hung out to dry, by the United States.

On Sunday, the front page of France’s Journal du Dimanche, a weekly newspaper, bore the headline: “Why Trump Threatens Us.” The “us” in question was both France and Europe. Coinciding with Trump’s visit, Le Monde has been running a series on the growing transatlantic divide, beginning with “The Europe–United States Divorce: Tensions in the Western Family.” French commentators noted that Trump was also shunning the Paris Peace Forum, a kind of Davos for multilateralism that opened Sunday. While it was inaugurated by Macron, Merkel, and the secretary-general of the United Nations, Trump was outside Paris at another American military cemetery, where he offered brief remarks.

The sense of Europe’s and the world’s growing distance from the United States, under a president who is a committed unilateralist, also echoed in the optics of the commemoration on Sunday morning. While Macron, Merkel, Recep Tayyip Erdoğan, Justin Trudeau, and more than 80 world leaders and leaders of major world organizations arrived in buses, walking solemnly in the rain together to take their place under the Arc de Triomphe, Trump arrived solo, in his own motorcade.

Others also arrived alone, including Benjamin Netanyahu and Vladimir Putin, who was the last to arrive. And there may have been security concerns involved. But Trump’s solitary arrival felt even more freighted, yet another sign of how under Trump, the United States intends to go it alone, pulling out of international multilateral treaties and starting trade wars with allies. French television commentators called it “symbolic” that the U.S. president shunned the group, and also noted, as Trump stiffly took his place next to Merkel, that “he didn’t look very smiley.” He was more smiley when Putin arrived. The Russian president gave Trump a thumbs-up and a brief, friendly pat on the arm.

Donald Trump smiles as Vladimir Putin arrives at the Arc de Triomphe, while other world leaders look on. (Benoit Tessier / Reuters)

In a somber speech beneath the Arc de Triomphe, Macron recalled how with World War I, Europe almost committed suicide. He said “old demons” were resurfacing and history was threatening to repeat itself, and threatening Europe’s history of peace. He decried “the selfishness of countries that regard only their own interests,” which sounded like a remark clearly aimed at the United States. “Patriotism is the exact opposite of nationalism,” he said. “Nationalism is its betrayal. In saying ‘Our interests first and others don’t matter,’ we erase what is most precious to a nation, what makes it live, what makes it great, what is most important: its moral values.” It was impossible not to hear Macron’s words, before so many other world leaders, as aimed at Trump, a sign of how the rest of the world is contending with the repercussions of “America First.”

In his speech, Macron called on nations to work together to fight climate change, poverty, hunger, sickness, and inequality. He said victory over “counter-truths” and “obscurantism” was in our power. And he concluded by saying: “Long live peace between people and between states. Long live the free nations of the world. Long live friendship between peoples. Vive la France.”

Vive la France indeed. This was very much Macron’s show, a way of positioning himself on the world stage as a uniter of Europe, a force against populism, ahead of elections for the European Parliament in May. It was also a chance for Macron to shore up the postwar Franco-German alliance. On Saturday, while Trump stayed in Paris doing whatever he was doing, Macron and Merkel went to Compiègne, a site outside Paris freighted with 20th-century history. It is the site where Marshal Ferdinand Foch, the supreme commander of the Western Front, signed the cease-fire agreement with Germany, ending World War I, and where Adolf Hitler forced France to sign a capitulation agreement in 1940.

It was the first time two leaders of France and Germany had met at the site since that year. The defining image of the day, of Merkel and Macron clasping hands in the rain before a dark-gray marble war memorial, was a potent symbol of Franco-German unity, a reminder of how the European Union was created to help keep German, and French, nationalism in check. There was something moving, even melancholy, about the image. Merkel’s era is coming to an end. Macron’s popularity has been flagging at home, and his pro-EU message may not be heeded. Right-wing forces are on the rise in France and across Europe, and have been calling for more national sovereignty and stronger borders. The photo already felt like an image from the past, a snapshot of the end of an era rather than the beginning of a bright new one. In inaugurating the Paris Peace Forum on Sunday, Macron said it was up to today’s leaders whether the images from the Armistice Day commemoration would be interpreted in the future as “a symbol of lasting peace between nations, or of the last moment of unity before the world falls into a new disorder.”

And then there’s Europe’s sense of distance from, even abandonment by, the United States. What had set Trump off upon his arrival in France was a radio interview Macron had given on November 6, in which the French president said Europe needed to step up its own defense in case of aggression from Russia and also because the United States announced that it would withdraw from the Intermediate-Range Nuclear Forces Treaty, which required the United States and Russia to eliminate certain missiles and weapons systems.

Elsewhere in the radio interview, Macron had talked about cyberthreats. “We are being shaken by hacking attempts in our cyberspace. We have to protect ourselves with respect to China, Russia, and even the United States of America,” Macron said. Some press reports conflated Macron’s two remarks, leading to the impression that Macron wanted Europe to set up its own army in case of attacks from the United States. “Very insulting, but perhaps Europe should pay its fair share of NATO, which the U.S. subsidizes greatly!” Trump tweeted.

On Friday, before Trump arrived in Paris, insulted Macron by tweet, and skipped his planned visit to the American cemetery, John Bolton, the national-security adviser, tried to downplay the clash of worldviews between the two leaders. “I don’t think the president or 99 percent of the people in the United States view things through a lens of saying, ‘This is multilateral, or that’s unilateral, or this is plurilateral,’” Bolton said in a small briefing in Paris. “I think from the president’s perspective, it’s very, very practical, which is, ‘What is the best way to protect the vital interest of the United States?’”

World War I was the first time American soldiers fought on European soil, after joining late in the game. “From the American perspective, of course, we were never isolationists, since we were creating a country moving west. We just weren’t Atlantic-facing, or as Atlantic-facing as some wanted,” Bolton said. He drew his own lessons from World War I. “I think the enduring lesson for the United States is, when you become a global power … you have global interests to protect.”

Back at the Arc de Triomphe on Sunday morning, the ceremony organized by Macron was appropriately somber. Yo-Yo Ma played a Bach cello suite. High-school students read testimony from accounts of World War I soldiers. The Beninise singer Angélique Kidjo belted out a song of gratitude. The European Union Youth Orchestra played “Boléro” by Ravel, who fought in World War I. It rained. After his speech, the speech decrying nationalism, Macron stood surrounded by soldiers in uniform and lit a commemorative flame. He was a man alone. But at least on his watch, the lessons he drew from World War I would not be forgotten.

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