Can America run the world without allies? That, in essence, is the question raised by US president Donald Trump’s decision to pull out of a painstakingly constructed international agreement to restrain Iran’s nuclear ambitions.

The unilateral exercise of US power is an idea that has long attracted John Bolton, the White House’s newly appointed national security adviser. Speaking in 2000, Mr Bolton suggested: “If I were redoing the [UN] Security Council today, I’d have one permanent member because that’s the real reflection of the distribution of power in the world.”

Now Mr Bolton is working for a US president who shares his dismissive attitude to international co-operation. In pulling the US out of the Iran nuclear deal, Mr Trump has rejected personal entreaties from the leaders of France, Germany and the UK.