Open this photo in gallery Prime Minister Justin Trudeau and U.S. President Donald Trump arrive to take part in a plenary session at the NATO Summit in England, on Dec. 4, 2019. Sean Kilpatrick/The Canadian Press

It was impressive that Prime Minister Justin Trudeau could smile and repeat his answer while chewing on a mouthful of radioactive waste.

It was served up by U.S. President Donald Trump, who last week ordered the major manufacturer of critical N95 masks, 3M, to stop shipping the items to Canada. And on Sunday, according to Ontario Premier Doug Ford, U.S. authorities had blocked a shipment of 500,000 masks, and the province was looking at running out of supplies in a week.

Every time a reporter asked Mr. Trudeau about it on Monday, he talked about constructive conversations with U.S. officials, and that Canada expects shipments to be delivered.

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It can be maddening to watch Mr. Trudeau in zero-info mode. On the other hand, one has to admit that the discipline in his robotic repetition of optimistic blank phrases is impressive.

The goal was to cajole the U.S., in a lobbying effort that’s been going on almost a week, to let those key supplies go. But the underlying mantra is Don’t Poke the Bear.

Mr. Trudeau and his team were painstakingly trying to avoid offending Mr. Trump.

Mr. Trump, after all, is the president who said he would help Democratic state governors fight coronavirus, but “they have to treat us well.”

So Mr. Trudeau’s warning on Friday was just to call the export restrictions a “mistake.” And on Monday, the PM kept smiling, after provincial premiers unleashed a chorus of boos for Mr. Trump.

Newfoundland Premier Dwight Ball said he was “infuriated” and noted the province housed stranded American travellers after the Sept. 11, 2001, attacks. Saskatchewan Premier Scott Moe called Mr. Trump’s actions a betrayal. Mr. Ford said at times like this, “you can see who your friends are.”

By Monday afternoon, there was a glimmer of hope: An Ontario order of 500,000 protective N95 masks, which had been sitting in a 3M warehouse in Illinois because the company could not get approval to ship it across the border, had been cleared to go.

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And then a bigger breakthrough: On Monday night, 3M said it had struck a deal with the White House to bring in millions of masks from China, so it could continue to ship N95 orders to Canada.

The 3M announcement doesn’t mean Canada will be exempt from all restrictions on exports of medical equipment, but it appears it will avert a looming shortage.

Mr. Trudeau’s low-key style is deliberate, similar to the stay-calm, be-cautious approach used during North American free-trade talks. Mr. Trudeau’s team doesn’t mind when premiers fire a few blasts at Mr. Trump, but they don’t want to want to pique the President.

The effort to persuade the U.S. to keep medical equipment flowing began days before 3M made public its concerns about cutting off exports of masks on Friday, according to a government source. The Globe is not identifying the source because the person was not authorized to speak publicly.

It involved calling many of the same contacts that the Canadian government used to press its case over trade talks. The message that Mr. Trudeau delivered on Friday, that it was a mistake to stop cross-border health co-operation because 1,500 to 2,000 nurses and doctors cross the border each day to work in Detroit or upstate New York, had been part of the talking points used by Canadian officials in speaking to U.S. counterparts for a few days. But they made the case quietly, behind the scenes, for fear that making it public might amount to picking a fight with Mr. Trump at a critical time.

Despite the appeals for cross-border co-operation, there was fear Mr. Trump would dig in his heels. The U.S. is facing the world’s largest number of COVID-19 cases and Mr. Trump has come under fire for failing to deliver equipment to key centres of the epidemic in the U.S. Mr. Trump invoked the Defense Production Act to order 3M to prevent the export of N95 masks. After 3M expressed concerns about cutting off countries like Canada, citing “humanitarian” reasons, the President expressed his ire at the company at a White House briefing.

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The release of the 500,000 N95 masks ordered by Ontario has therefore sparked some optimism inside the government. U.S. officials haven’t provided assurances that Canada will get the exemption from export restrictions that it is seeking.

But Canadian officials have had to mount a major campaign with U.S. officials, while Mr. Trudeau forces himself to keep smiling, carefully trying to avoid poking Donald Trump.