Barely seven months ago Donald Trump was in China on an all-singing state visit, during which two key priorities emerged. The first — his concern with North Korea’s nuclear threat and his keenness that Chinese president Xi Jinping should help defuse it — has all but evaporated after the US-North Korea peace summit a fortnight ago.

The second — the US-China trade deficit — was outlined in emollient language last November. Yet, over recent weeks, the US president has rechannelled his protectionist aggression, announcing a total of $253bn of tariffs on Chinese goods, sparking retaliatory measures from Beijing. Two-way tariffs covering steel, aluminium and some agricultural goods have already been introduced.

Sunday’s announcement by the People’s Bank of China that it would release more than $100bn of commercial bank reserves as an economic stimulus has been presented largely as a response to the trade spat. But it has a far broader back-story — and far more profound implications, both for China’s vast finance sector, and for Wall Street.