MONTREAL — When Justin Trudeau first met Donald Trump face-to-face last February, the contrast between the Canadian prime minister and the American president couldn’t have been any sharper. Mr. Trudeau, worldly and dapper, can barely open his mouth without extolling Canada’s cheery multiculturalism or its open-border globalism. Mr. Trump lurches from thinly concealed xenophobia to America-first protectionism by way of insults and tirades.

Yet Mr. Trudeau survived their meeting and has remained in Mr. Trump’s good graces ever since. “I like the prime minister very much,” Mr. Trump told a gathering of his supporters last December. “Nice guy. Good guy.”

Mr. Trudeau’s smooth relationship with Mr. Trump hasn’t only kept the North American Free Trade Agreement negotiations alive, if teetering. It is also one of the main reasons that, after just over two scandal- and gaffe-prone years as prime minister, Mr. Trudeau remains far and away the most popular political figure in this Trump-adverse country.

Canada’s obsession with Mr. Trump’s whims and overindulgences goes beyond morbid curiosity.

Despite differing views on the metric system and the occasional far-flung war, the United States and Canada have enjoyed more than 150 years of benign relations. Yet Mr. Trump’s frequent threats to scuttle Nafta are seen here as an existential threat to Canada’s economy, which sends over 75 percent of its exports to the United States.