Let’s leave aside the lists and the spreadsheets that may or may not see the light of day; the accusations, the recriminations and the more or less sordid details. The first question I asked after the caravan of sex claims moved on from Harvey Weinstein’s shower, via Kevin Spacey’s bedroom, to the UK’s corridors of power, was a bit more basic: what on earth possessed them?

What on earth possessed a minister, Mark Garnier, to ask his personal assistant to buy him what were primly referred to as sex toys? (Did he pay? In cash? Surely they did not go on expenses?) What on earth possessed Stephen Crabb – his party’s rising star, who had thrown his hat in for the Tory leadership as an exemplary family man – to start “sexting” a young woman who was not his wife?

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And before him, what on earth possessed Brooks Newmark MP to send naked pictures of himself to a woman (who turned out to be a reporter). What was going through his head when he took those photographs? What encouraged him to think that his physique, or parts of it, were worth a photograph? What made him then press the “send” key? Did he ever consider that the recipient might not share his enthusiasm – or, more to the point, that she might shop him if it all went wrong? He had to be well aware of the power of social media, as that’s how he had composed and sent his messages.

Not that any of this starts or stops with social media, of course; it has merely made a lot of things much easier, including clumsy flirting, intimidation and bullying. Men (and women) have been aware for at least a generation not only that a whole spectrum of behaviour – from unwanted overtures to sexual assault – could be a social liability in a way it once might not have been, but that the risk of being found out was much greater, because the other party might be less shy of speaking out. Social change, including feminism, gay rights and the decline of deference, have all played a part in that.

So why, oh why, do they risk it? With Weinstein & co, there are reasonable answers. They have power, they have money, they have lawyers, and they know (from experience) that they can get away with it. Or they knew it until recently. Their power not only to hire and fire, but to make and break careers, especially in showbusiness, gave them power to have their way.

But politicians? Some may indeed have power, money and lawyers at their disposal, but most don’t. Yet there seems to be a greater proportion of MPs likely to behave badly in this particular way than might be found in the population at large. Nor, for all that the political sex scandal has a long and dishonourable history in Britain, is the genre unique to this country.

Bill Clinton was known for philandering – “a hard dog”, as Hillary described him, “to keep on the porch”. But there were also darker stories about him, of coercion and unequal dalliances. Paula Jones accused him of exposing himself in front of her in a hotel room. And his relationship with Monica Lewinsky, the White House intern, came close to ending his presidency. As the man most guarded and watched in the whole of the United States, what went through his mind when he first summoned her to the Oval Office? That everyone would turn a blind eye?

François Mitterrand managed to keep not only a mistress but a child secret for the whole of his 14-year presidency

François Mitterrand managed to keep not only a mistress but a child secret for the whole of his 14-year presidency (which may say as much about French mores or the docility of the French media in those years as it does about politicians’ behaviour). Jacques Chirac was a source of grief to his long-suffering wife, Bernadette; while François Hollande risked nocturnal scooter trips from the Elysée Palace to visit his mistress in a flat across town.

One way or another, they got away with it. Not so Dominique Strauss-Kahn, who lost his job as head of the IMF and his chance of the French presidency, over claims by a maid at a New York hotel that he sexually assaulted her – which were eventually dropped but resulted in an out-of-court settlement. Further allegations later emerged, suggesting a pattern of behaviour.

So what is it about politicians? Theirs is a career where reputation is crucial and where the price of disgrace – this particular sort of disgrace – tends to be higher than it would be in other walks of life. Once found out, even if they do not step down voluntarily, their chances of de-selection are high. But do some of the traits that incline someone to a political career incline them also to risky behaviour, especially of a sexual nature?

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Across countries, continents even, it seems to me that there are features common to many successful politicians. High on the list would be personal charm – the French say that a candidate for office, especially for the presidency, must “seduce”. Persuasiveness also comes in, of course. And added to this is often an element of vanity, even narcissism, which convinced them they were electable in the first place, even against quite considerable odds. And when that self-belief is justified by victory at the ballot box, maybe it encourages another piece of risk-taking, and so on.

In one of his text messages, Stephen Crabb told the young woman this: “Most MPs are risk-takers to one degree or another. Usually in the areas of money, sex, political opportunism. Add in the adrenalin, the attention u get, and the time away from family … toxic mix.” Those words suggest something else many politicians have in common: a high level of self-awareness – which has a habit of emerging only when it is already too late.

• Mary Dejevsky is a freelance writer and broadcaster