OTTAWA — Shortly after his election in late 2015, Prime Minister Justin Trudeau declared “Canada is back,” promising a renewed Canadian presence on the world stage.

Trudeau has taken political hits since then for minor lapses, such as a luxury family holiday visit to a Caribbean island and an ill-fated trip to India, but his biggest challenge, just a year before Canadians go to the polls, has come from the leader of Canada’s longtime military ally and economic partner.

Now, Canadians worried that their government has been sidelined in crucial trade talks and may be forced to back down on important economic issues, having been outmaneuvered by President Trump and possibly sold out by an erstwhile Mexican ally.

Several rounds of tense discussions about the North American Free Trade Agreement (NAFTA) culminated Monday in a trade pact that excluded Canada, prompting Foreign Minister Chrystia Freeland to cut short a trip to Europe and dash to Washington for the first trilateral trade talks with the United States and Mexico in five weeks.

“Until this week, Canadians thought they had a special place with America,” said Nik Nanos, a leading pollster here. “But for Donald Trump, the fact that Canada and the U.S. have had a strong cordial relationship and a close shared history is not relevant.”

Canadians are keenly aware of their country’s “asymmetrical economic relationship” with the United States, and that in general the United States has 10 times the population and 10 times the influence.

“The U.S. is much more important to Canada than Canada is to the U.S.,” Nanos said.

Yet Canadians are proud, even nationalistic at times, happy to boast of their kinder, gentler public discourse, their single-payer health-care system, their low crime rates and their stricter gun laws. And when Trudeau became prime minister, many Canadians reveled in the international attention Canada received for its handsome, self-styled “feminist” leader.

The Canadian public soured on the United States after Trump’s election. Asked in an Environics Institute 2018 World Survey about what country they considered a “positive force in today’s world,” only 11 percent of Canadians polled named the United States, compared with 15 percent in 2008.

And then Trudeau and Trump clashed. After the Group of Seven summit in Quebec in June, Trudeau criticized U.S. tariffs on Canadian aluminum and steel.

“Canadians, we’re polite, we’re reasonable, but we also will not be pushed around,” he said a news conference.

Trump responded by insulting Trudeau, calling him “dishonest” and “weak.” Canada was excluded from NAFTA talks soon after that, but Canadians rallied around the prime minister, vowing to boycott U.S.-made products and cancel holidays in the United States.

A survey by Nanos Research showed that 71 percent of Canadians surveyed approved of Trudeau’s handling of the trade file.

But for Trudeau’s political opponents, the latest turn in the negotiations is proof of their contention that he doesn’t have the substance needed to be prime minister.

“This shows that the Trudeau government blew it over the past year,” Erin O’Toole, a member of the opposition Conservative Party, said on CTV. “You always want to be at the table for any deal, let alone the most important deal for our economy.”

But the latest turn in the talks makes the “no deal” option particularly dangerous for Canada if Trump goes ahead with his threat to impose tariffs on Canada’s substantial exports of cars and automotive components to the United States.

That means Trudeau may be forced to cede on issues such as the protection of Canada’s dairy sector and the Chapter 19 dispute settlement process, unless the United States and Mexico decide this week that a deal with Canada is essential, giving the Canadians more leverage than they appear to have now.

Asked to comment on the NAFTA talks Tuesday, Trudeau said Canada is “encouraged” by the progress made in the discussions between the United States and Mexico, “particularly on autos.”

“We will engage in a positive and constructive way, as we always have been, and look forward to ultimately signing a deal as long as it’s good for Canada,” he said, “and good for middle-class Canadians.”