Woody Allen once mused: “What if everything is an illusion? In that case, I definitely overpaid for my carpet.” Foreign buyers of US assets have long appeared curiously untroubled by such doubts. But the warning signs for them – and dollar bulls – are swiftly becoming unmistakable.

Take the US current account deficit, which was a stubbornly high 6.6 per cent of gross domestic product in the second quarter. Individual releases should always be taken with a pinch of salt, but together with downward revisions for the first quarter, however, they are a reminder of just how much growth would have to slow to close the current account gap. As a result, US obligations towards the rest of the world will continue to grow.