Pity Jay Powell. The man who appointed him as chair of the US Federal Reserve wonders whether he is a bigger enemy of the US than China’s president, Xi Jinping. Donald Trump entered new territory by implying his country’s central bank was run by a traitor. Previously, Mr Trump had described Mr Powell as “clueless” and a man with a “horrendous lack of vision” who is like a “golfer who cannot putt”. Also he “maybe” regrets having picked him. 

Anyone would think Mr Powell was trying to ruin Mr Trump’s re-election prospects. In fact, most of Mr Trump’s recent epithets came after the Fed had done what he wanted by cutting interest rates in late July. His tweet followed an otherwise anodyne speech in which Mr Powell sounded a mildly dovish tone about the Fed’s likely trajectory. His offence, it appears, was to sound agnostic about how far the Fed should go to counteract the fallout from a trade war that is harming domestic growth. Though the Fed chair was too diplomatic to single out America’s escalating trade war with China, Mr Trump correctly sensed that this was the unforced error to which the Fed chair was referring.

Where does it go from here? At the best of times, US presidents have limited power to stop a recession, or even a growth slowdown. Mr Trump has already ruled out two out of the three most obvious things he can do to to keep the economy buoyant ahead of next year’s election. The first would be to call off his trade war with China. The likelihood that it will get worse has spurred a flight to the dollar, which has more than wiped out any depreciatory effect of last month’s quarter point interest-rate cut.