The purpose, wrote a fan of Bertillon’s, is “to give each human being an identity, an individuality, certain, durable, invariable, always recognisable”. That, at least, Mr Trump can already claim to have achieved.

To appear as an entitled child who has just been told to go to his room, boiling inside and swearing vengeance against those who did him wrong. That’s his identity, that’s how we recognize him.