People who are worried by the prospect of President Donald Trump are often reminded of the checks and balances in the American system. The US president is not a dictator. He is constrained by the constitution, the courts and the Congress.

But there is one area where checks and balances do not apply: nuclear weapons. Dick Cheney, the former US vice-president, explained the situation clearly in 2008, when he told an interviewer: “The president of the United States for 50 years is followed at all times, 24 hours a day, by a military aide carrying a football that contains the nuclear codes that he would use and be authorised to use in the event of a nuclear attack on the United States. He could launch the kind of devastating attack the world’s never seen. He doesn’t have to check with anybody. He doesn’t have to call the Congress. He doesn’t have to check with the courts.”

The president’s powers are even more extensive than those described by Mr Cheney. The US is not committed to a doctrine of “no-first-use” of nuclear weapons. So Mr Trump could order a nuclear strike against an adversary, even if the US itself had not been attacked.