Leading article: Blair's bloody bequest

Possibly one of the less significant consequences of the destruction of the twin towers in New York, five years ago tomorrow, is that it marked the beginning of the end of Tony Blair's time at No 10. In retrospect, we can see that it was the point at which he began to diverge from the British people, who had only just re-elected him with a second huge majority. Until that point, New Labour had been astonishingly successful in embodying the mood and values of a rejuvenated nation.

More relevant to last week's political turbulence, 11 September 2001 was the moment when Mr Blair's path began to diverge seriously from his own party's. It was not evident at the time, because he performed so well, with such an instinctive grasp of the enormity of what had happened. Indeed, he seemed better able to express the sense of shock felt by Americans and the rest of the world than the US President himself.

But, as David Runciman writes on page 33, he also became utterly fixed in his conviction that standing shoulder to shoulder with the American people meant supporting in public whatever response to the atrocity George Bush decided. Looking back, the warning was there. We will not rest, he declared, "until this evil is driven from our world". It was easy at the time to put it down as hyperbole, but it seems he really meant it.

Thus Britain was locked into supporting an American policy that was fundamentally misconceived. From the start Mr Bush called it a war, which was precisely the legitimation the deranged sociopaths of al-Qa'ida sought. They think they are at war, and they want to be called warriors, but it was a terrible error to take them at their own estimation. The excessive reliance on high-altitude bombing in the war against the Taliban in Afghanistan, and the failure to catch Osama bin Laden, also helped add stature and perverse glamour to the jihadist cause. This newspaper distinguishes emphatically, of course, between the justified and lawful removal of a government that harboured terrorists in Afghanistan, and the invasion of Iraq that followed 15 months later. But the war in Iraq helped to undermine the moral legitimacy of the Western military presence in Afghanistan, and did more than anything else to strengthen the hand of jihadist terrorism across the world. Only yesterday, a CIA report concluding that Saddam Hussein had no connection with al-Qa'ida was finally published. The US-British invasion has turned Iraq from a country that had little to do with terrorism into its clearing house.

Thus the British military mission in Afghanistan, from being a relatively successful and justifiable theatre of the war on terror, has become contaminated and risks becoming yet another military entanglement too far, with no clear route out of the mountains. As we report today, British generals are increasingly open in their frustration that the disaster of Iraq is wiping out all they have gained in Afghanistan. Unfortunately, there is no question that in Afghanistan the imperative is to give the military the resources needed to finish the job. At least there are grounds for hope there, whereas in Iraq there is no guarantee that more troops would improve the situation - even if it remains the best judgement that withdrawing our troops would make matters worse.

This is what the war on terror has come to: many more people killed by terrorists, especially in Iraq, and many people who were not terrorists killed by US, British and other forces in their attempt to prosecute a military campaign against an abstract noun. The Independent on Sunday today compiles the best estimate of the minimum total cost over the past five years: 62,006 killed, 4.5 million refugees and more US taxpayers' dollars than could pay off the debts of every poor nation on earth.

Most of those totals are accounted for by Iraq, the single word with which Mr Blair will always be most identified. Britain's part in that disastrous war is much of the reason why Mr Blair will be leaving office in the next few months rather than serving out most of the full third term as he had hoped. It has discredited the UK, and, worse, discredited the very idea of liberal interventionism. And it has obscured much of the good that he has achieved. The question of when precisely he goes is much less important, therefore, than that of what his successor can do to try to make amends for the mistakes of the past five years.

That is why last week's attempt to force Mr Blair out was so misconceived. Neither the plotters nor the intended beneficiary of their plotting, Gordon Brown, have told us how he would begin to get Britain and the world out of the mess that Messrs Bush and Blair have got us into. Thus their manoeuvring looked as if it were simply machine politics in pursuit of personal ambition - the sort of thing that brings politicians into disrepute.

An important, if unintended, consequence of the attempted coup, however, was that it makes a contested election for the Labour leadership more likely. That is necessary and desirable. It would provide Mr Brown and his challenger, whoever that might be, with the chance not just to answer the character questions posed by Charles Clarke but to set out, freed from collective responsibility, a radical new direction in foreign policy. Only by winding down the rhetoric of war, by distancing Britain from the delusions of the American right wing and stressing the primacy of patient, intelligence-driven police work, can we begin to contain and diminish the threat from jihadist terrorism. The British people deserve to hear from those who aspire to be prime minister how they propose to deal with Mr Blair's bloodstained legacy.