OTTAWA — For President Obama, foreign trips these days have increasingly become an exercise in explaining the inflamed politics of his country to nervous foreigners.
So it was here on Wednesday, when Mr. Obama joined the leaders of Canada and Mexico at a summit meeting that began as a show of North American solidarity and ended up as an attempt to repudiate the nativist and isolationist currents that are agitating politics in the United States, as well as in Europe.
With the gothic spires of Canada’s Parliament as a backdrop, Mr. Obama, Prime Minister Justin Trudeau of Canada and President Enrique Peña Nieto of Mexico announced a landmark agreement on climate change and extolled the benefits of a Pacific Rim trade agreement. But it was the charged words in the American election and Britain’s departure from the European Union that seized most of the attention.
Mr. Obama deplored the anti-immigrant remarks of Donald J. Trump, the presumptive Republican nominee, particularly his statements about Mexican immigrants. Though he never mentioned Mr. Trump by name, Mr. Obama said the next American president would have a strong interest in having a solid relationship with “our good neighbor to the south.”
Speaking at a news conference with the Canadian and Mexican leaders after their meeting, the president said that anti-immigrant appeals had a long history in the United States, but that they had never permanently curtailed the flow of people into the country.
“We should take some of this rhetoric seriously and answer it boldly and clearly,” Mr. Obama said, answering a question from a Mexican journalist, “but you shouldn’t think it is representative of how the American people think.”
Mr. Obama said he rejected the argument that the harsh tone in the American presidential campaign, or in Britain’s recent referendum on leaving the European Union, was populist. He ridiculed the notion that a candidate who worked to preserve the interests of wealthy people could be a populist.
“They don’t suddenly become populist because they say something controversial in order to win votes,” Mr. Obama said. “That’s not the measure of populism; that’s nativism or xenophobia or worse. Or it’s just cynicism.”
Mr. Peña Nieto, for his part, put Mr. Trump in a line of populist demagogues, including Hitler and Mussolini, though he, like Mr. Obama, did not use the candidate’s name. “Those political actors, by using populism and demagoguery, they choose the easiest way to solve the challenges of today’s world,” he said.
Their comments lent urgency to the North American leaders’ summit meeting, a diplomatic ritual that usually goes unnoticed by the public. This meeting, in fact, slipped from being an annual gathering during the administration of George W. Bush to once-every-few-years during Mr. Obama’s presidency.
For Mr. Trudeau, who has inherited Mr. Obama’s mantle as a change agent, the meeting was a sort of debut on the global stage. He presented the deal under which Canada, the United States and Mexico pledged to generate half their power through clean energy sources by 2025. To achieve that goal, they will seek to harmonize energy regulations, increase energy efficiency and reduce emissions of methane, a greenhouse gas.
Under Mr. Trudeau’s conservative predecessor, Stephen Harper, Canada pulled out of its commitments to the first global climate pact, the Kyoto Protocol, and clashed with the United States over Mr. Obama’s opposition to the Keystone XL oil pipeline. But Mr. Trudeau has recommitted Canada to legislative efforts to combat climate change, much as Mr. Obama did when he succeeded Mr. Bush in 2009.
For Mr. Obama, the visit was a chance to galvanize three major economies behind the advances made in the Paris climate-change accord, at a time when Britain’s vote to leave the European Union has clouded the prospects for multilateral cooperation and the durability of international agreements.
Mr. Obama said he worried that Britain’s exit from the European Union would freeze investment in the country and in Europe. The leaders also discussed the impact of Britain’s vote on trade agreements. Mexico and Canada are signatories to the Trans-Pacific Partnership, the mammoth Asia-Pacific deal that has stalled in the United States, with Hillary Clinton, the presumptive Democratic nominee, and Mr. Trump both coming out against it.
Appearing with Mr. Peña Nieto on Tuesday, a day before Mr. Obama’s arrival, Mr. Trudeau said, “We’ve seen around the world many examples of protectionism, of stepping away from trade agreements and engagements like we’re showcasing today.”
In a speech to the Canadian Parliament later in the day, Mr. Obama acknowledged that globalization had unleashed deeply disruptive forces.
“While the circumstances of Brexit may be unique to the United Kingdom,” he said, “the frustrations that people feel are not.” But an interconnected world, he argued, was irreversible. The remedy was to pursue policies like the Trans-Pacific Partnership, which would level the playing field.
Mr. Obama’s relations with Mr. Harper were tense, and the president had not visited Canada since 2010. With Mr. Trudeau’s election, however, the chill has given way to an affectionate big-brother relationship. In March, Mr. Obama celebrated Mr. Trudeau during a state visit to Washington that felt at times like a passing of the torch.
“He campaigned on a message of hope and of change; his positive and optimistic vision is inspiring young people,” Mr. Obama said. “On the world stage, his country is leading on climate change and cares deeply about development, so from my perspective, what’s not to like?”
This summit meeting is being marketed as a meeting of “three amigos.” But Mr. Obama is spending less time in Ottawa than Mr. Trudeau did in Washington. After his speech to the Parliament, at which he received a rapturous reception, Mr. Obama flew home, not spending a single night in the Canadian capital.
Like most countries with a larger and more powerful neighbor, Canada has a general wariness toward the United States and its political leaders. As a result, Canadian prime ministers have generally been careful to be seen as friendly but not too cozy with American presidents.
However, there appears to be little danger of that for Mr. Trudeau when it comes to Mr. Obama. Throughout Mr. Obama’s presidency, he has not only been Canadians’ favorite American politician, he has also enjoyed higher ratings than Canadian politicians. One poll released on Wednesday found him more popular even than the charismatic Mr. Trudeau.
Perhaps more surprisingly, the fondness of Canadians for Mr. Obama transcends party lines.
Christine Campbell and her husband, Rob, woke up at 5 a.m. on Wednesday to travel from Perth, Ontario, into Ottawa to wait along Mr. Obama’s motorcade route. While she voted for Mr. Harper’s Conservatives during Canada’s election last October, she said that she had always admired Mr. Obama and that she hoped Mr. Trudeau took some tips from the American president.
“Trudeau is just starting out, he’s learning the ropes,” Ms. Campbell said as she stood at an intersection where the motorcade would soon turn. “Possibly Mr. Obama will be a good mentor for him.”