There were many things that could have derailed the summit of the increasingly divided NATO alliance. Few, however, could have predicted that it would be a video of Prime Minister Justin Trudeau gossiping with other leaders about Donald Trump that would send the U.S. President storming home early from an otherwise successful meeting.

The 29-member alliance averted the worst on Wednesday by persuading Turkey to drop its threat to veto an updated plan for the rapid defence of Eastern Europe, allowing Secretary-General Jens Stoltenberg to declare that NATO’s all-for-one mutual defence pledge remains intact. It was a positive moment for an alliance that has recently seen its unity strained by internal friction, as well as questions over how to deal with Russia.

But an end-of-summit communiqué hailing the North Atlantic Treaty Organization’s “solidarity, unity and cohesion” went little noticed as Mr. Trump grabbed headlines with his broadside at Mr. Trudeau and early departure.

“He’s two-faced,” Mr. Trump said of Mr. Trudeau when asked if he had seen the video, which was recorded by an ABC News cameraman on Tuesday evening during a reception for NATO leaders at Buckingham Palace.

“Honestly, with Trudeau, he’s a nice guy,” Mr. Trump continued after a pause. “I find him to be a very nice guy. But you know, the truth is that I called him out on the fact he’s not paying 2 per cent, and I guess he’s not very happy about it.”

Mr. Trump, who has rattled the alliance with a years-long campaign to get NATO’s other members to pay more for their own defence, said during a bilateral meeting with Mr. Trudeau on Tuesday that Canada was “slightly delinquent” for not meeting NATO’s military spending target of 2 per cent of gross domestic product.

Mr. Trump made his remarks about the Buckingham Palace video during a scheduled tête-à-tête with German Chancellor Angela Merkel that followed the conclusion of the main leaders’ meeting. Shortly afterward, he announced that he would not give a scheduled postsummit news conference with international media, and would instead head straight back to Washington, where he is facing impeachment hearings.

In the Buckingham Palace video, Mr. Trudeau was captured chatting and laughing with French President Emmanuel Macron and British Prime Minister Boris Johnson about Mr. Trump’s penchant for long, rambling news conferences. Dutch Prime Minister Mark Rutte and Princess Anne were also present during the conversation, although Mr. Trudeau did most of the talking.

In a 26-second clip that went viral, Mr. Johnson asks Mr. Macron: “Is that why you were late?” before Mr. Trudeau cuts in: “He was late because he takes a 40-minute press conference off the top,” Mr. Trudeau said, chuckling between sips of a beer.

“His team’s jaws just drop to the floor,” Mr. Trudeau added in apparent reference to Mr. Trump’s aides.

Mr. Trudeau later explained that he saw jaws drop among Mr. Trump’s staff when the President, during an unexpectedly long news availability at the start of their bilateral meeting on Tuesday, made the surprise announcement that next year’s NATO summit would be held in the U.S. at Camp David.

“We were all surprised and I think pleased to learn that the next G7 will be at Camp David. I think that was an unscheduled announcement and … I think every different leader has teams who every now and then their jaws drop at unscheduled surprises, like that video itself for example,” Mr. Trudeau said during his own postsummit news conference.

Mr. Trudeau expressed remorse that the Buckingham Palace video had distracted from the substance of the NATO gathering.

“I think the lesson is always that this is an important meeting, at which we had significant achievements in unity, in thoughtful approaches to the future of NATO, where we came out strong and united. To endeavour to keep the focus on the substantive issues that were discussed … is something that we’re all going to try to do a little harder.”

In the video, only Mr. Johnson, who can be seen glancing at the camera, seems aware of the possibility that the exchange was being recorded. On Wednesday, Mr. Johnson claimed that the leaders weren’t even discussing Mr. Trump – something Mr. Trudeau contradicted by acknowledging that they were indeed discussing the U.S. President.

Mr. Trump has attacked Mr. Trudeau’s character before, calling him “very dishonest and weak” after last year’s Group of Seven summit in Charlevoix, Que., after Mr. Trudeau criticized U.S. tariffs on Canadian steel and aluminium in a news conference held after Mr. Trump had already departed.

Conservative foreign-affairs critic Erin O’Toole said he fears that Mr. Trudeau’s unguarded comments will damage top-level Canada-U.S. relations at a time when Ottawa needs Washington’s help on matters such as the detention of two Canadian citizens in China.

“Behaviour like this is not giving us any ability to advance an agenda with a very difficult and mercurial U.S. President,” he said.

Christopher Sands, a senior professor of Canadian Studies at Johns Hopkins University, said the incident appears to have confirmed Mr. Trump’s earlier criticisms of Mr. Trudeau.

“My view is that President Trump made his mind up about Justin Trudeau at Charlevoix … and now has been confirmed in this impression because Trudeau was nice to Trump face to face and then catty about him with Macron later,” Prof. Sands said, referring to the G7 summit in Quebec.

“This is not good for their personal relationship,” he added.

He predicted that there would not be an “explicit price for Canada to pay now” because lower-level officials and the “machinery of government” continue to handle much of the bilateral relationship.

Mr. Trump’s angry response to the Buckingham Palace video was only the latest salvo at a NATO summit dominated by chippy remarks. Ahead of the meeting – which was supposed to celebrate the 70th anniversary of the alliance that won the Cold War – Mr. Macron grabbed headlines by suggesting that NATO was “experiencing brain death” and unable to deal with challenges including Turkish military adventurism in Syria and an unpredictable U.S. administration.

Those words irked both Turkish President Recep Tayyip Erdogan and Mr. Trump, who labelled Mr. Macron’s comments “nasty.” Mr. Trump and Mr. Macron held an icy bilateral meeting on Tuesday that saw the U.S. President suggest that he could send “some nice ISIS fighters” to France – a reference to members of the Islamic State that have been captured on the battlefields of Syria and Iraq.

Before arriving in London, Mr. Erdogan also said he planned to block an updated plan for the defence of Eastern Europe unless the other members of the alliance accepted Turkey’s position that the Kurdish YPG militia was a “terrorist” force, something France and other countries have refused to do. The YPG has been a key NATO ally in the battle to drive the Islamic State from its previous strongholds in Syria.

On Wednesday, the Turkish veto threat evaporated, and the plan for Eastern Europe – which will see Canada assign six fighter jets and a frigate to a rapid-response force that will remain based in Canada, but deployed to Poland and the Baltic states in the event of a crisis with Russia – was unanimously approved.

The Globe and Mail, December 4, 2019