"I'm afraid that Hillary Clinton suffers from pseudologia fantastica," said my friend the psychiatrist. The would-be president of the United States is not one of his patients: this is what might be described as an informal diagnosis, provoked by Mrs Clinton's extraordinary claim to have dodged sniper-fire in Bosnia in the service of her country.

She made the remarks in a speech at George Washington University – that's George Washington as in "I cannot tell a lie, father".

The speech was to an audience chock-full of generals and admirals – and Mrs Clinton was clearly determined to demonstrate that she was up to being their commander-in-chief: "There was a saying around the White House that if a place... was too dangerous, the President couldn't go, so send the First Lady instead. So that's where we went. I remember landing under sniper-fire. There was supposed to be some kind of greeting ceremony at the airport but instead we just ran with our heads down to get into the vehicles to get to our base."

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When reporters and others who accompanied Mrs Clinton on that 1996 trip protested that nothing of the sort happened, she grimly stuck to her tale: "We had to be moved inside because of sniper fire. There was no greeting ceremony. Now, that is what happened."

Unfortunately for Mrs Clinton, after a few days of her increasingly irate dissembling, CBS started broadcasting its 12-year-old tapes of the then First Lady landing at Tuzla airport.

It showed the following : No sniper fire. No running for cover – heads down or otherwise. Instead we see Mrs Clinton – accompanied by daughter Chelsea – taking part in a charming greeting ceremony, receiving a bunch of flowers from an eight-year-old girl. Just for the record, husband Bill had flown in to Tuzla some months earlier (minus Hillary) when it actually was a bit "dangerous".

Faced with this avalanche of incontrovertible facts, Mrs Clinton finally collapsed into teenagerish incoherence: "You know, I think that a minor blip, you know, if I said something that, you know, I say a lot of things – millions of words a day – so if I misspoke, that was just a misstatement." Yes, dear.

Alas for her long-suffering supporters, Hillary Clinton has form: this is by no means an isolated incident.

A couple of weeks earlier she had boasted that: "The role I played [in the Northern Ireland peace process] was instrumental." Her spokesman added, just in case we failed to get the point: "We would not have peace today if it had not been for Hillary's hard work in Northern Ireland."

The former Ulster Unionist leader David Trimble – who with John Hume won the Nobel Peace Prize – showed great self-restraint in describing Mrs Clinton's claims as a "wee bit silly". I spoke about this to Tony Blair's ex-chief of staff Jonathan Powell, who was genuinely "instrumental" in the peace process: with all the tact of a former diplomat he said that he wouldn't comment on Mrs Clinton's claims "because I don't want to tell a lie".

Like her bizarre account of dodging bullets in Bosnia, Mrs Clinton's claims to have played a critical role in the Northern Ireland peace process are intended to mesh with her now notorious "attack ad" against Barack Obama, which insisted that only she possessed the character and experience to handle a "3am call to the White House" if America's security were to be suddenly threatened.

Given that Mrs Clinton's latest excuse for her "misspeaking" over her Bosnia escapade is that she was suffering from "sleep deprivation", Americans might reasonably wonder if she would just scream at the 3am caller from the Pentagon : "Have you any idea what the time is?" – and then slam the phone down.

My psychiatrist friend tells me that one of the characteristics of pseudologia fantastica – or pathological lying, in more vernacular language – is that the sufferer tells fibs even when there is no obvious gain to be achieved. He – or she – just wants to be thought to be a much more interesting person.

This, presumably, would explain Mrs Clinton's excited claim, in the immediate aftermath of the World Trade Center attacks, that she was a very worried mother because daughter Chelsea was jogging in the vicinity "when the plane hit".

Later, Chelsea revealed that throughout the entire horrifying episode she was (along with the rest of us) "staring senselessly at the television". Then there is Mrs Clinton's long-held insistence that she was named after the conqueror of Everest, Sir Edmund Hillary. Given that Sir Edmund's successful ascent of Everest took place six years after Hillary Clinton's birth, we can see that myth-making is at the very heart of her sense of identity.

To some extent, this is true of all of us. Memory is not put down like video-tape: we constantly rewrite it, according to our psychological needs. The bigger our need for self-justification, the more we reconfigure our past. This is what lies behind Nietzsche's remark that pride always defeats memory when we do something wrong.

Yet Hillary Clinton's fantastically careless reconstruction of her past, now that it has been exposed by the unforgiving videotape of CBS, is a crushing blow to what remained of her chances to defeat Barack Obama.

After all, the essence of her attack on Obama was that he was a fantasist, a mere purveyor of wishful thinking, and that she was the no-nonsense, down-to-earth realist who could deal with the world as it is.

She has not yet given up on this. Yesterday, her spokesmen reminded us that in his speech last year at Selma, Alabama, Barack Obama had claimed that his parents had got married – and that he had been born – as a result of the great Selma to Montgomery civil rights march: "There was something stirring across the country because of what happened at Selma, Alabama, because some folks are willing to march across a bridge. So they got together, and Barack Obama Jnr was born. So don't tell me that I don't have a claim on Selma, Alabama."

The problem with this, as Mrs Clinton's spin doctors gleefully point out, is that the Selma marches occurred in 1965. Barack Obama Jnr was born in 1961.

This is actually an interesting observation about Obama's own self-invention – but has no power coming from such a deeply tainted source.

It is desperate, last-ditch stuff to respond to accusations of fantasising self-aggrandisement by saying, in effect: So what? My opponent lies in exactly the same way that I do.

No, Mrs Clinton can not recover from her debacle at George Washington University. It only remains for us to wonder what little Hillary would have said if her father had asked her who had killed the cherry tree in the family garden.

Perhaps: "I cannot tell a lie, father. I did cut it with my little hatchet – but only out of self-defence because its branches were attacking me."

d.lawson@independent.co.uk

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