There is the theory that President Trump is still bitter about his Canadian hotel ventures that went bust.
Some, on social media, have speculated that a 2019 photograph in which Justin Trudeau appeared poised to kiss Melania Trump, the first lady, at a Group of 7 gathering in France, left Mr. Trump with a grudge against the dashing Canadian prime minister.
And then there is the transactional view, that Mr. Trump sees the acquisition of Canada as the 51st state as the ultimate real estate deal that would seal his presidential legacy.
As Mr. Trump prepares to push ahead with a new round of tariffs on the United States’ neighbors to the north and south, he has expressed a special brand of loathing for Canada. The bullying of a country whose most prominent stereotype is that its people are “nice” has led to political upheaval in Canada and created both consternation and speculation about why Mr. Trump wants to engage in a trade war with one of America’s biggest trading partners.
“I can’t quite figure it out,” said Stephen Moore, the Heritage Foundation economist and former adviser to Mr. Trump. “Whether it’s some kind of strategic leverage, I don’t know.”
Noting that there is “no love lost” between the president and Mr. Trudeau, Mr. Moore added: “With Trump, politics is personal.”
Mr. Trump has threatened to hit Mexico and Canada with 25 percent tariffs on all imports on Tuesday unless the countries do more to prevent migrants and drugs from flowing into the United States. On Saturday, the president picked another trade fight with Canada, this time over lumber.
Intrigue abounds in Canada about why Mr. Trump has repeatedly belittled a neighbor and threatened to destabilize its economy with tariffs, a process that has brought relations between the two countries to a low point not seen in decades.
In contrast to the close and supportive relationship that Mr. Trudeau, who is entering his final week in office, enjoyed with another U.S. president, Barack Obama, his relationship with Mr. Trump has been fractious.
In 2018, following the Group of 7 summit meeting in Charlevoix, Quebec, Mr. Trump heckled Mr. Trudeau on social media, accusing him of being “very dishonest and weak” and of making up “false statements” while suggesting that he might impose tariffs on Canadian-made autos.
While Mr. Trudeau was generally circumspect in his public remarks about Mr. Trump during the president’s first administration, the two men have dramatically different personal and political styles. Mr. Trump bombastically denigrates people he perceives as opponents, whereas Mr. Trudeau often speaks about the value of bringing people together, what he once called a “sunny ways” approach to political life.
In candid remarks to a group of business leaders last month that was captured by a microphone, Mr. Trudeau offered a theory for Mr. Trump’s Canada obsession that is widely shared in the country.
“Not only does the Trump administration know how many critical minerals we have, but that may be even why they keep talking about absorbing us and making us the 51st state,” Mr. Trudeau told the gathering in Toronto.
“They’re very aware of our resources,” Mr. Trudeau said, “of what we have, and they very much want to be able to benefit from those.”
He added: “But Mr. Trump has it in mind that one of the easiest ways of doing that is absorbing our country. And it is a real thing.”
Mr. Trump does have a particular affinity for minerals. He has been pushing to broker a deal to secure access to Ukraine’s supply of rare earths as he seeks to broker an agreement to end its war with Russia.
As a businessman, Mr. Trump had two dealings with Canada that, while relatively limited, were both failures. The Toronto hotel and condominium project, owned by a Toronto investor who licensed the Trump name and hired a Trump company to manage it, went into receivership in 2016. The following year, a hotel owned by Malaysian investors bearing the Trump name, again under license and with a similar management contract, opened in Vancouver, British Columbia. (Promotional material exaggerated the building’s height.) It failed, as well.
Both hotels, which now operate under different names and management, were magnets for protesters in a country where Mr. Trump has long been unpopular for his “America First” views and disparagement of Canada. Before the Vancouver opening, the city’s mayor at the time, Gregor Robertson, wrote to the building’s owners asking that they not use the Trump name on it.
“Trump’s name and brand have no more place on Vancouver’s skyline than his ignorant ideas have in the modern world,” Mr. Robertson wrote.
Before delving into politics, Mr. Trump expressed little ill will toward Canada.
In 2012, when the Obama administration was delaying a decision on approving the Keystone XL Pipeline, which would have transported oil from Canada to the United States, Mr. Trump declared on social media that the project must move forward.
“We need to use our resources and support allies like Canada,” Mr. Trump said.
But by 2015, his perceived failings of the North American Free Trade Agreement between the United States, Canada and Mexico became a central issue of Mr. Trump’s first presidential campaign. Mr. Trump routinely called the deal a “disaster” for American workers, and prioritized scrapping the pact as a first order of business if he won the election.
An agreement to overhaul the trade deal was signed in 2020 after fraught negotiations between the three countries that often grew contentious. At one point, Mr. Trump suggested leaving Canada on the sidelines and proceeding with a deal between the United States and Mexico.
Now back in office, Mr. Trump has made clear that the agreement he signed did not do enough for the United States and must be rewritten. In recent days he has lashed out at Chrystia Freeland, the Canadian official who negotiated it on behalf of Canada.
“She’s a whack,” Mr. Trump said of Ms. Freeland, who was Canada’s deputy prime minister and finance minister during the president’s first term, in an interview with The Spectator.
As Mr. Trump has wielded the threat of new tariffs on Canada over the last month, his tone toward the departing prime minister has been even more derisive. He has nicknamed Mr. Trudeau “governor” amid persistent suggestions that the United States might annex Canada.
Mr. Trump even called for the former Canadian hockey player Wayne Gretzky to run for prime minister, suggesting late last year that he would “win easily.” Mr. Gretzky, who does not support Canada’s joining the United States, has faced backlash at home from citizens who view him as a traitor because of his association with Mr. Trump.
The insults have led to a boom in nationalism in Canada, including “Made in Canada” Facebook groups. In one group, which has more than a million members, Canadians compared notes on pancake mixes that are made in Canada and offered recommendations on flavors of Cove Soda, a potential alternative to Coca-Cola.
“There’s a generalized sense of patriotism that has not been evident in Canada in many years in response to Trump and Trump’s hostility,” said Ira Wells, a professor at the University of Toronto’s Victoria College.
But Mr. Trump appears unfazed by Canada’s declarations of independence. He indicated last week that the United States was also prepared to sever ties with Canada without changes to the trade relationship between the two countries.
The United States, Mr. Trump said, has no need for Canadian products such as lumber, and he asserted that Canada could not survive without American military protection and favorable trade terms.
“I love Canada, I love the people of Canada,” Mr. Trump said at a cabinet meeting at the White House. “It’s not fair for us to be supporting Canada — If we don’t support them, they don’t subsist as a nation.”