Can a country ever be too big to fail? Waiting for global stock markets to open this morning felt grimly reminiscent of the beginnings of the sub-prime lending crash, the moment many finally understood the old cliche that when the US sneezes, everyone catches a cold. But when it threatens to hack its nose off with a chainsaw, before changing its mind at 10 minutes to midnight, then nobody knows where they stand.

The world’s biggest economy is now experiencing what looks like its very own Liz Truss moment, only this time in a country powerful enough to take everyone else down with it. If the US really is prepared to keep playing this mad game of chicken – threatening ruinous tariffs against Mexico then postponing them, sowing fear and discord constantly among its allies – that risks creating the kind of all-American supernova that sucks everyone into a black hole.

Canada, which a few weeks ago was sending firefighters to help battle the Los Angeles wildfires, was told it wouldn’t just be whacked with tariffs but would be punished to a point where it “ceases to exist as a viable country” and submits to becoming the 51st state of its aggressive neighbour. “Much lower taxes, and far better military protection for the people of Canada – AND NO TARIFFS,” Trump declared on his Truth Social platform. Also, no sovereignty. Magnanimously, the president has said he wouldn’t actually invade Canada – more reassurance than Denmark got when it rejected demands to hand over Greenland – but merely use economic force to similar ends.

The demeanour of both the outgoing prime minister Justin Trudeau and the probably incoming........

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