As is often the case when dealing with Donald Trump, the saga of the five million N95 respirators built by Minnesota’s 3M Co. and purchased by Ontario keeps changing.

On Saturday, the U.S. President invoked the Defense Production Act to force the Maplewood, Minn.-based multinational to stop sending Canadians the suddenly precious pieces of medical personal protective equipment, which are considered the gold standard for personal protection when viral droplets start to fly.

Saturday night, the level of concern on this side of the Medicine Line was starting to ratchet up — Alberta Premier Jason Kenney posted one of his little social media homilies about how unhappy he was with President Trump.

“As a Canadian, I am insulted by the decision announced today to block the export of critically needed medical equipment that we need to fight the pandemic here in this country,” he intoned. “Apparently we can’t even count on our closest friend and ally to be a supplier.”

Yesterday morning, Canadian politicians were understandably starting to get wound up, with both Prime Minister Justin Trudeau and Ontario Premier Doug Ford assailing the United States.

Mr. Ford said Ontario had only a week’s supply of the masks on hand. Later in the day, Mr. Kenney said Alberta only had a month’s supply — contradicting earlier carefully worded reports by Alberta health officials that they had a three- to four-month supply of medical supplies and “slightly less” when it came to N95 respirators. Health care workers were frightened.

Yesterday evening, 3M was widely reported to have issued a news release saying it would continue to export the U.S.-made medical face masks to Canada. The deal with the White House is said to hinge on a plan by 3M to import more than 166 million of the masks from a facility it owns in China.

“Canada looks to have secured a vital supply of face masks from the United States,” the National Post, champion of globalization, sighed with relief. Mr. Ford’s estimate of the original shipment size was adjusted to half a million.

But don’t count on it that all won’t change again tomorrow — because Donald Trump.

That’s that way it plays when a country forgets Lord Palmerston’s famous dictum — “We have no eternal allies, and we have no perpetual enemies. Our interests are eternal and perpetual, and those interests it is our duty to follow” — and ties itself too closely to the empire next door.

Of course, Lord Palmerston, later prime minister, was home secretary of Britain when he uttered those famous words in 1848, and Britain was the empire next door. Sometimes pursuing your country’s interests — at least pursuing them unsubtly — is not an option if you don’t happen to be the only Imperial power on the block.

That, of course, is Mr. Trudeau’s problem, and that of those lesser first ministers too, given our relative size and relationship with The Neighbours, as a Polish colleague of my father used to call his country’s “fraternal allies” to the east back in the 1970s.

Everyone understands that what President Trump was proposing was an embargo — an act of war, in other words, and embargoes of food and medical supplies are war crimes to boot.

Mr. Trudeau and his deputy, Chrystia Freeland, can hardly say that aloud, though, without risking dangerous repercussions. They understand, as a columnist for the Toronto Star put it yesterday, “we don’t have a North American ally any more,” we’re dealing with “a sick gorilla in a cage.” Anything could happen, and if we take a wrong step it probably will.

So what can we do about it?

Not much for now, other than stepping very carefully.

Longer term, maybe we can be a little less enthusiastic about those globalizing “trade” deals that Liberals and Conservatives alike seem to love so much.

Obviously, we need to create our own secure supply of medical equipment like N95 masks — even Mr. Kenney concedes that. But the “secure” part of that equation means they must be made by a Crown corporation, because we can never — literally never — trust a private corporation not to go broke, close down and move somewhere else, or sell out to someone who doesn’t have our interests at heart.

And maybe now that we’ve been threatened with the receiving end of one of the United States embargoes, we can stop jumping aboard so enthusiastically every time President Trump or whoever succeeds him decides to embargo some other country because it won’t bow to the Washington Consensus, be that Russia, Iran or Venezuela.

And maybe, here in Alberta, the next time we have a dust-up with British Columbia over a pipeline project we can stop threatening to boycott shipments of vital supplies to them. Although, at least in that case, we have Canadian courts that can step in and encourage Premier Kenney to act like a grownup.