KEY POINTS:
Bill Clinton famously claimed that he tried marijuana once but "did not inhale". Amazingly enough this wasn't necessarily Slick Willie's most preposterous public statement. Years later he would stare into the camera and intone, "I did not have sex with that woman" when even a Mongolian goatherd knew otherwise.
(Apparently he was invoking some entirely private distinction between oral sex and the real thing.)
Later still he stonewalled a grand jury with: "It depends on what the meaning of the word 'is' is."
The lesson of Clinton's career and enduring popularity would seem to be that if the public finds a politician attractive and decides he can be trusted not to steer the ship of state into the proverbial iceberg, they're not too bothered by whatever low-rent grubbiness he gets up to in his down-time.
That in turn suggests they care even less about the sins of his hot and foolish youth.
However, at this point the pundits are reserving judgment on what impact the revelations of David Cameron's and Barack Obama's teenage drug-taking will have on their electoral prospects.
Cameron is the leader of the British Conservative Party and, unlike his hapless three immediate predecessors, someone the British public might just regard as Prime Minister material.
At Eton he got a severe wigging from the headmaster for smoking marijuana, but the experience wasn't sufficiently salutary to stop him further indulging while at Oxford University, coincidentally the setting for Clinton's mythical feat of self-denial.
Obama, the junior senator from Illinois who this week confirmed that he's running for president, has admitted using marijuana and cocaine when he was at high school and in the grip of an identity crisis.
As usual there's more to both furores than was immediately apparent.
Obama actually 'fessed up 11 years ago when an astute publisher decided there was a market for the autobiography of the first black person to be elected editor of the Harvard Law Review.
Dreams From My Father details his unusual background - Kenyan father who returned to Africa when Obama was 2; white Kansan mother; brought up, largely by his grandparents, in Hawaii - and his struggle to come to terms with his mixed ethnicity.
Obama's candour has been applauded but it remains to be seen if this baggage becomes a burden when the campaign gets nasty, as it assuredly will.
The buzz around Cameron is heightened by the fact that he's a toff. This week the Independent dwelt on his membership, while at Oxford, of the Bullingdon Club, an exclusive clique under whose aegis blue-blooded undergrads have engaged in binge drinking and vandalism for 150 years.
While the story might have helped Cameron secure the football hooligan vote, its real subject is his social class rather than a youthful predilection for getting blotto and heaving pot-plants through restaurant windows.
The implied question was: do we really want this upper-class twit to be our next Prime Minister?
For those of us who don't share the English obsession with class, the question is: why do we care what politicians did before they became politicians?
We don't in relation to judges, school teachers or airline pilots, to take three professions in which it's arguably more relevant.
Oddly enough this view that our political leaders should have avoided the pitfalls of youth co-exists with the widespread assumption that they're all dishonest, inept, parasitic sleazebags whose real motivation for entering public life is to feather their own nests. Censoriousness and cynicism make uneasy and illogical bedfellows.
As usual too, the focus on backgrounds and peccadilloes obscures the real issues. Dabbling in drugs didn't distract these two from their studies or slow their meteoric rises. In fact, that sense of having risen without trace is the real question mark hanging over this pair, both of whom so far seem more about style than substance.
Cameron had been in Parliament for only four years before becoming leader of a party persuaded by successive electoral calamities that the essential attribute of a would-be Prime Minister is that he shouldn't remind people of their dorkiest uncle. A similar notion seems to have precipitated National's recent change of leadership.
Obama has been a senator for two years. His inexperience may not matter, for just as "presentation" skills increasingly outweigh achievement in the appointment process, presidential elections are usually won by the best campaigner as opposed to the best candidate.
And while editorial writers agonise over whether the US is ready for a black president, the anti-PC brigade senses a conspiracy unfolding: if Obama was white, they bleat, his candidacy wouldn't be taken seriously.
Looking at the extremely mixed bag of Caucasians who've occupied the White House or got within a heartbeat of the presidency (Dan Quayle, to take one admittedly striking example), one wonders how they manage to keep a straight face.
