Rex Tillerson proved a hapless US secretary of state. On the evidence so far, his successor Mike Pompeo will turn out to be a thoughtless steward of America’s global interests. Throw in President Donald Trump’s ego-obsessed mood swings and you have the end of American diplomacy.

Mr Tillerson knew little about affairs of state — a lifetime in the oil business did not bestow understanding of the geopolitical tides of the times. His promised reform of the state department became an exodus of top-flight diplomats. He never gained Mr Trump’s confidence. From time to time he was able to restrain the president, but he was more frequently undermined by Twitter storms from the White House.

Mr Pompeo is closer personally to Mr Trump — perhaps because he so studiously mimics the president’s weaknesses. Both imagine the US can do what it likes, where it likes, when it likes — an assumption paraded by Mr Pompeo in his approach to Iran’s nuclear efforts. Neither man asks, let alone answers, the question at the heart of all diplomatic calculations: “and then what?”