Two days after John F Kennedy was shot in 1963, the headmaster of a Cambridge school at which I was teaching delivered such an impassioned threnody to the assembled pupils that he reduced many of them to tears. Especially moved by the fact that, like the president, he himself was a former naval officer aged forty-six, he depicted Kennedy as little less than a martyr and a saint. When I tried to prick the emotional bubble by reminding my class that the president had almost precipitated a nuclear holocaust, I merely provoked more weeping.

Of course, the lamentations were loudest in America, and immediately after his assassination Kennedy became the subject of eulogies the like of which had not been seen since the death of Lincoln. Two hagiographical accounts in particular, by Theodore Sorensen and Arthur Schlesinger Jr, portrayed Kennedy as a kind of King Arthur, presiding over Camelot with wit, wisdom, courage and panache. He was, said Sorensen, ‘the brightest light of our time’. His administration, according to Schlesinger, marked one of the most shining moments in history. The Kennedy family did their best to complete his canonisation, promoting plaudits and stifling criticism. The writer William Manchester was so harried by the Kennedy family’s lawyers and private detectives that he compared the experience to an encounter with Nazis.

Not long after his death, Kennedy’s reputation plummeted. The Pentagon Papers and other official documents exposed the president as a dangerous Cold Warrior. Further publications showed him to have been in many respects the son of his corrupt, scheming, foul-mouthed father, Joe. Jack was a ruthless power seeker, a friend