What Monica Lewinsky was for Clinton the Hutton inquiry is for Tony Blair

Monica did not end Clinton's presidency, but the scandal created an irrevocable impression that he was not to be trusted

It doesn't matter what the Hutton inquiry finds. It is providing ghoulish entertainment sure enough, and all of us in medialand are gripped; but the damage to Tony Blair is already done. This is not Blair's Watergate: he will survive, and win the next election. The Hutton inquiry is, rather, Tony Blair's Monica Lewinsky moment: survivable, but corrosive of his public image, even in the eyes of his supporters. Like his friend Bill Clinton during Zippergate, he has not suffered a lethal attack. Something more subtle has happened: a serious wound to the leg that will leave him limping forever.

Monica, Ken Starr and the oral sex revelations did not end the Clinton presidency. They did not even seriously damage Clinton in the polls; if he could have run for a third term, he undoubtedly would have won. But the scandal created an irrevocable impression that Clinton was not to be trusted. The President had deployed every weapon of mass persuasion he had - the fierce gaze, the husky voice, the slow finger-wagging, Hillary hitting the chat-shows with charges of "a vast right-wing conspiracy" - in a battle that turned out to be based on a lie. The British people have now concluded that our Prime Minister too used all of his own special magic on an equally false cause, so the magic will never work again. Nobody will take to the streets about this; few people will even want to see him drummed out of office; but every statement he makes from now on will be slightly less effective and slightly more doubted.

Even in the best-case scenario for the Government - if there is a judgement that there was no political interference with the dossier and no government pressure on David Kelly at all - there will still be no WMD in Iraq. There will be no absolution in the court of public opinion now, short of a massive and extraordinary discovery in a bunker outside Baghdad. The departure of Geoff Hoon or even Alastair Campbell will not absorb much, if any, of the bruising inflicted on Blair.

This is a tragedy for Blair personally. The idea that he is a con artist is manifestly false. Paddy Ashdown's diaries reveal that Blair was fretting about Iraq's WMD in private conversations with the Liberal Democrat leader as long ago as 1998, back when George Bush was the governor of Texas and nobody was contemplating a second Gulf war. I agree with Michael Foot - hardly an ardent defender of Blair - who told me in an interview: "I haven't the slightest doubt that Blair was sincere." He added: "It was a terrible mistake, but a terrible mistake honestly made."

It's not hard to see how the Prime Minister talked himself into believing that Saddam had WMD. Nobody disputes that at the time the weapons inspectors left Iraq in 1998, Saddam had enough "growth media" to produce 26,000 litres of anthrax and 1,200 litres of botulinium toxin, not to mention 550 mustard-gas filled shells, and 400 biological-weapon capable aerial bombs. You don't have to be Richard Nixon bent on war to extrapolate from this that there really were still some weapons in Iraq in 2003; Blair did not convince himself of something that was transparently absurd, as some people are now claiming.

But still, the WMD argument should never have been made, because, in the end, the evidence was far from conclusive (indeed, most of it has turned out to be just plain wrong), and it certainly did not justify the cast-iron certainty that Blair claimed to have. For whatever reason, it now seems obvious that Saddam really didn't have any WMD. It is time for Blair to come clean about this. His continued insistence that they will be found is beginning to look ridiculous.

And the awful truth is that Blair could have acted on his convictions and supported the war without any of this nonsense. Blair went into this with the best of intentions. It is just silly to claim that Blair cooked up all these arguments to justify a grab for oil, or a straight-forward imperialist project. No, the formative foreign policy experience for Blair was the Kosovo war. His motives in that conflict were quite clearly a humanitarian concern to prevent a programme of ethnic cleansing being carried out on the continent of Europe. The undoubted success of the Kosovo campaign - Milosevic on trial, Kosovo on track to democracy, the refugees back in their homes - shaped Blair's approach to foreign policy forever.

I have no doubt that Blair saw the conflict in Iraq largely through the prism of Kosovo. A Kosovo-ending seemed plausible: Saddam on trial, Iraq on track to democracy, and the 4.5 million Iraqi exiles free to return home. This is still eminently achievable. That surely seemed like enough good reason to participate. The motives for Blair going into Iraq are actually very similar to the reasons why he has doubled the international development budget since he came to power, or dedicated so much time to Northern Ireland: a desire to do good. As he put it in his speech to Congress: "If we are wrong [about WMD], we will have destroyed a threat that, at its least, is responsible for inhuman carnage and suffering."

Yet Blair should have been candid about this from the beginning. Imagine if he had come before the British people in January this year and said, "Okay, so the Americans are worried about weapons of mass destruction in Iraq. They might be there; they might not; the truth is, nobody knows. But what we do know for sure is that Saddam Hussein's tyranny is monstrous, and every possible indicator suggests that the Iraqi people want our help in overthrowing him. We should have backed them in 1991 when they rose up. Go talk to George Bush senior and John Major about that evil failure."

Sipping from a "Things Can Only Get Better" mug, he could have continued: "Our attempts to contain Saddam since the last Gulf war have been a disaster. He is manipulating our sanctions regime to kill even more people and to tighten his grip. I will not have the death of another half a million people on my conscience. We cannot end sanctions without ending Saddam's rule, because he can't be trusted with the extra resources that would flood into Iraq. The only alternative to this ongoing nightmare is to back the Iraqi people and overthrow him. So let the Americans worry about the WMD Saddam might or might not have developed; we are worried for the Iraqi people. Their need is great enough for us to support this war on those grounds alone."

But that is a war that, alas, will never be fought. Instead, we are stuck in the squalid fog of argument about the WMD that never were. And all the while, trust in Blair is slipping away. The political ramifications are too vast to measure. The Europhobic press was yesterday exultant at this damage. "Loss of trust in Blair stalls poll on euro," jeered one Canadian-owned paper. There are so many issues on which Blair still needs to persuade the British people, and so much left for him to do. Yet from now on, he will be talking to a public that is holding its nose to block out the gangrenous smell of his festering WMD-inflicted wound.

j.hari@independent.co.uk