As Trump has learned in recent months, the man in the Oval Office cannot simply issue a decree changing, say, the US healthcare system. He has to build majorities in the House and Senate, which is harder than it looks. If he wants to change immigration policy, a mere order is not enough. He can be stopped by the courts, as Trump saw with his travel ban. But if he wants to rain fire and fury on a distant enemy, bringing more fire and fury down on his own citizens and many hundreds of millions of others, there is no one standing in his way. Not for nothing does the geopolitical literature refer to the US president as the “nuclear monarch.”

The more you hear of the simplicity of the system, the more frightening it becomes. If Trump decides he has had enough of Kim Jong-un’s verbal threats, he merely has to turn to the low-level military aide at his side and ask them to open up the black briefcase that officer keeps permanently in their grasp. The bag is known as the nuclear “football”. (It gets its name from the code word for the very first set of nuclear war plans: dropkick.) Inside the bag is a menu of options, explained in detail in a “black book,” but also set out in a single, cartoon-like page for speedy comprehension. Trump has only to make his choice, pick up the phone to the Pentagon war room, utter the code words that identify him as the president and give the order. That’s it.