Whose problem is it anyway? As the dollar sank to new lows this week, a growing number of people began to question how long the US can remain relaxed about its weak currency.

The US has a long (if not unbroken) tradition of indifference to dollar weakness, dating back to John Connally, the Nixon-era Treasury secretary, who famously told a group of visiting Europeans that the dollar was “our currency, but your problem”. The official line today is that the US has a “strong dollar” policy. But it does not appear to mean much beyond support for a market-determined exchange rate.