The decision to take his or her country to war is the gravest that a prime minister can make. It puts at risk not only the lives of the country's troops, to say nothing of the lives of foreign nationals (civilians and conscripts), but also the country's future security and international goodwill. We have the right to expect our leaders to agonise over the decision, to consider every possible means of avoiding it, to pore over all the available evidence bearing upon it, to ask searching questions about the reasons given for going to war.
For Tony Blair now to say that the world is better off without Saddam Hussein in power borders on frivolity. The world would be better off without many current rulers - including, some would say, Ariel Sharon and George W Bush. The questions Mr Blair had to answer were: why this particular ruler and why now? He published a dossier on how the dictator posed an imminent threat to British interests, emphasising that publishing such intelligence material was unprecedented, and implying that it represented a fraction of what was available to him. That was the centrepiece of his case for war. It has now collapsed. The war, however virtuous its results in other respects (and even that is a matter of dispute), was unnecessary according to the criteria that Mr Blair himself set. It was the biggest decision of his period in office and he got it wrong. If a Tory premier had been responsible for misjudgement on such a scale, it is hard to believe that a Labour Party in opposition would not now demand his resignation.
Lord Butler, in the careful way of a Whitehall mandarin, has avoided denouncing individuals and, in particular, avoided impugning their integrity. That is probably right. It is up to MPs and voters to apportion blame. But Lord Butler's report provides ample evidence of what went wrong.
One of the prime functions of the intelligence services in 2002 was, as the report puts it, "to inform planning for a military campaign". Much of this intelligence was necessarily speculative, concentrating on the worst-case possibilities that could follow an invasion, and in particular on what Saddam might do if he faced defeat. A Joint Intelligence Committee assessment completed on 9 September 2002, from which Lord Butler quotes substantial extracts, was clearly written as an exploration of the risks involved in war. Some of the material turned out to be wrong, but the intelligence services were right to include it as a warning. It quite explicitly stated that Saddam was not likely to use WMDs pre-emptively. Yet two weeks later, these assessments, stripped of many caveats and of nearly all context, were translated into a dossier designed to advocate the case for war. The WMDs that Saddam might possess and might use during a war became WMDs that he almost certainly possessed and would, in time, unleash in an unprovoked act of aggression.
This was the origin of the notorious claim - which was repeated four times in the published dossier and interpreted by a tabloid paper as a potential attack on "British servicemen and tourists in Cyprus" - that Saddam could launch chemical and biological weapons within 45 minutes. The 9 September assessment reported that such weapons (if they existed) "could be with military units and ready for firing within 20-45 minutes". The context and wording make it clear that the reference was to battlefield weapons. Transposed into a dossier attempting to make the case that Saddam was a dangerous aggressor, they appeared as weapons that could be used against civilians - as both Mr Blair and Geoff Hoon, the Defence Secretary, apparently thought they could be.
It may seem astonishing that senior ministers did not grasp the nature of the material crossing their desks. But by that stage, they were viewing it through only one prism: the urgent importance of overthrowing Saddam. Mr Blair was almost certainly sincere when he said he was "in no doubt" that the threat from the Iraqi dictator was "serious and current". He had been reading, judging from the extracts published by Lord Butler, about anthrax, botulinum and sarin, free-fall bombs and airborne sprays, attacks on Bahrain, Jordan, Qatar, Kuwait, Israel and Turkey - all possibilities which, however remote, had to be considered if a war started. But Mr Blair apparently thought - or wanted to think - that these germs were ready to overwhelm the Middle East at any moment, perhaps even to strike down Londoners.
The Prime Minister's relationship with the truth has always been an uncertain one. He is a lawyer by trade, accustomed to convincing himself that a weak case can be won. He is also a politician who owes much of his success to deft presentation. As a BBC Panorama programme has recalled, Mr Blair told the Commons, during Operation Desert Fox in 1998, when cruise missiles and bombs rained down on Iraq, that the aim was "to degrade the ability of Saddam Hussein to build and use weapons of mass destruction". The operation was declared a success. Yet Brian Jones, then a member of the Defence Intelligence Staff, told Panorama that his department was not able to provide with any certainty a list of targets. John Morrison, deputy chief of Defence Intelligence from 1995-99, said that the operation wasn't "particularly effective", though he had been under pressure to say it was.
But as Nick Cohen argues (page 12), it is not feasible to prove that Mr Blair was lying, then or now. Nor is it necessary. He made a catastrophic misjudgement, which should be reason enough for a prime minister to stand down. The Butler report may be circumspect in its judgements, but it is not a whitewash. It reveals that, before he took his country to war, Mr Blair failed to do his job and, most alarmingly, seemed not to master his brief. MPs should now hold him to account.