Whatever the facts of the Lewinsky affair may prove to be, it is enough to doom Bill Clinton's presidency that people are willing to believe it could be true. The allegations are, quite literally, beyond belief: that a President of the United States, already under suspicion of sexual misconduct, could be so incontinent as to seduce a 21-year-old intern, so reckless as to risk the affair being discovered, and so criminally stupid as to lie about it under oath, and counsel others to do the same. The personality profile that emerges -- slave to momentary passions, devoid of concern for others, and cocksure of avoiding detection, or at least the consequences -- is the very definition of a psychotic.

Yet after all the many scandals and near-scandals that have beset his presidency, and before his presidency his candidacy, and before his candidacy his tenure as governor of Arkansas; and on repeated exposure to his non-denial denials, the cautious phrases that seem much but say little, not quite lying but not quite telling the truth, the public is all too ready to believe that he could have done what Monica Lewinsky says he did. Only this time it seems to matter to them.

The interesting question is: why? Why, if the press and the people were so willing to look the other way before, why, after all that they have excused and forgiven and explained away; why is it widely agreed that this time he may have gone too far? One reason, some have suggested, is that this indiscretion (if it be such) was committed while he was president -- as opposed, say, to the tangle of shadowy dealings surrounding the Whitewater land deal, which occurred while he was governor. But that is too neat a separation. As events have suggested, not only the ethical norms of Governor Clinton's Arkansas, but many of the same characters were simply transferred to the White House, en masse. Much of their time since then, it seems, has been spent trying to conceal what they were up to in Little Rock.

A second possible explanation is that, if indeed he urged Lewinsky that she should lie about the affair to lawyers for Paula Jones -- another figure from his Arkansas past, whose sexual harassment suit has made Clinton's sexual history a legal as much as moral issue -- Clinton would have broken the law.

People, it is said, were willing to overlook his vulgarity ("kiss it"), his compulsive infidelity (leaving aside the interesting legal question, as he reportedly put it to Lewinsky, of whether oral sex counts as adultery), even his tendency to prey upon employees. Certainly, many people like to believe that what a politician does in his private life is irrelevant to his fitness to hold office. It's not the sex, in this view. It's that he lied about it.

I don't think so. In this case, I think it's the sex. People expect him to lie.

What else was he going to do: confess? What has really shocked them is that he could have done the deed in the first place. It's the recklessness of it, the appalling lack of judgment. It's almost pathological. The public, perhaps, is less concerned that its leaders are liars, than that they should come to believe their own lies.

This may be more common than we believe. To succeed in politics at any level calls for a certain economy with the truth, though no more than is required in advertising or the law. But to endure the lifelong, non-stop campaign that is required of a would-be President of the United States -- even to want to -- entails a degree of deceitfulness, not to say monomania, that is a close approximation of insanity.

This is most pronounced in that succession of candidates who style themselves after John Kennedy, from Gary Hart to Joe Biden. Like Kennedy, each seems genuinely possessed of a soaring moral ambition, at least in his vision for the country. But, again like Kennedy, each seems equally assured that, by virtue of his historic destiny, he is relieved of the ordinary moral constraints that might apply to lesser men. And so each, in his vanity, is given to almost comical acts of deception and bravado: inviting reporters to catch him in an act of infidelity, or lifting whole passages from another politician's speech. Kennedy, in his day, could get away with it.

They cannot.

The same pattern is evident in Bill Clinton. What the experience ought to teach us is that there is no neat distinction to be made between private life and public life; that a man who will lie to his wife, easily and often, will lie to everyone else; that, in a phrase heard more often of late, character counts.