HE WAS the most famous member of one of the most power-hungry and ruthless families since the Borgias, possibly cheated his way into the White House and his main legacy to his country was the Vietnam War.

Yet we’re in the middle of a mini-raft of TV shows to mark the 50th anniversary of John F Kennedy’s ascension to power; goodness knows what it will be like when we get to the half-century of his assassination.

The main question is simply – why? What’s the big deal with JFK? We all know he pioneered style-heavy politics, but don’t we need some substance to justify the attention after all these years?

The two presidents who followed him were surely men of greater ability, but no one looks back with wistful yearning, or even the same prurient fascination, to Johnson or Nixon.

Ah but, you may say, that’s missing the point; it’s his death that made the difference. Of course it did, in more ways than one. For one thing, it gave rise to not merely one conspiracy theory, but a whole conspiratorial cocktail. The ingredients are all there: the president murdered, his apparent assassin killed, with possible suspects including the Russians, Castro, the Mob and the CIA.

Then his bright little brother is gunned down a few years later, and the rest of the “first family” self-destructs in various ways. You really didn’t need any links with Marilyn Monroe for this to be the kingpin of conspiracies.

I’m told some satellite channels dissect the “details” virtually on a loop. The only conspiracy to top it is the one about whether the moon landings happened or not – but then, didn’t JFK order the moon shots too?

His death also gave rise to a lingering sense of loss, of what might have been. True, he died before his inadequacies and errors could rebound on him, but also before he had any chance to put them right. We’ll never know what he might have done, and the idea still haunts many people, not only in America, of a great opportunity snatched away.

I think there’s something else, too. Kennedy died in 1963, which was a very odd year, not just because it produced the Daleks and the author of this article. The British poet Philip Larkin claimed it was the one in which sexual intercourse began “between the end of the Chatterley ban and the Beatles’ first LP”.

He could equally have mentioned the Profumo scandal for dealing moral blows to the old order, while the Fab Four’s success on both sides of the Atlantic helped to kick off the social and cultural ferment we think of as “the Sixties”.

Whether you see that period as the end of all that’s respectable and responsible and the start of a decadent slide downhill, or a time of liberation and an end to hypocrisy, 1963 was about when times started a changin’, like some kind of historical fault line, with JFK’s death running along the fracture. Epochs and eras are just human concepts, of course; but then, ideas have power.

Finally, consider this. The reputations of the three presidents before Kennedy remain pretty well intact, but it’s hard to think of any post-JFK incumbent, with the arguable exception of Reagan, who ended his term with dignity rather than disappointment, disillusion or even disgrace.

It’s almost as though the Kennedys, not content with being cursed themselves, left something toxic behind in the White House. Or is it down to the crushing weight of expectation created by a dream of leadership which promised so much and delivered so little?

Either way, if someone could lift the curse they’d be doing a massive favour to the American people, and maybe the rest of us too. Except, of course, the conspiracy theorists.