Donald Trump, we know, has forged a special bond with North Korea’s Kim Jong Un. We should forget Russia’s effort to subvert American democracy — Vladimir Putin is fine, just fine. Even European Commission president Jean-Claude Juncker turns out to be a good guy when it comes to talking trade. Now the US president says he is happy to meet his Iranian counterpart Hassan Rouhani. Last week he was threatening Tehran with all manner of fire and fury. Given the great deal Mr Kim got in Singapore, Mr Rouhani might do well to grab the offer.

You can see why all this might leave Beijing feeling edgy. Chinese president Xi Jinping was also once a recipient of the Trumpian best-of-friends treatment. But, as the crazy kaleidoscope that is US foreign policy keeps spinning, the White House war on Beijing’s trade policies is establishing itself as something of a constant. The president’s revised view of Mr Xi is that “he’s for them and I’m for us”.

Mr Trump has a point. Most of his generalised rage about trade is a measure of ignorance about globalisation and supply chains. He lives in the 1950s. In those days, things were made in one country — usually America — and then sold in another — preferably just about everywhere else. The modern world of bits and pieces, with components and semi-finished products moving to and fro across borders, does not fit the president’s template.