John Rentoul: So where, then, is the backlash? Who will speak up for Mr Kennedy?

The reason the Liberal Democrat leader's speech last week was received so badly was not just a matter of taste. What surprised me was that so many of those who opposed the war shied away from the crude allocation of blame. For so long Blair has been blamed for everything, from global warming to fat children. Yet suddenly, when something struck close to home, there was an instinctive realisation that the causes of terrible deeds are a bit complicated.

The more we know about the ideology that seems to have motivated the bombers, the more we realise that "Iraq" has been stripped of anything that might resemble a legitimate grievance and been twisted to fit an unreal story. Many opponents of the war accept that Blair and possibly even George Bush went into Iraq with the sincere intention of bringing freedom and democracy, but say that they were foolish or negligent in thinking that it would work. Very few readers of The Independent on Sunday think that the US and the UK invaded Iraq in order to humiliate and oppress Muslims. Yet that is what the followers of Osama bin Laden teach.

What is most enraging about President Bush's conduct of the so-called war on terror is his apparent determination to feed the jihadists' mythology. The report last week that the President overruled legal advisers to the US armed forces to allow "aggressive" interrogation techniques in Guantanamo Bay confirms that it was policy to insult the religion of detainees.

Yet, despite all the efforts of Bush and Donald Rumsfeld to mess it up, I still think that getting rid of Saddam Hussein was justified. It may be that joining the Iraq war has made Britain more of a target for jihadists than it would otherwise be. But where does that argument take us? To pulling out of Iraq, when most Iraqis, however reluctantly, want us to stay, fearing greater bloodshed if we go? To pulling out of Afghanistan? To deciding that we were wrong to have helped create the state of Israel and denying its right to exist? To ending the idea of equal rights for women? There is no point in starting down the road of appeasement.

It is worth noting that one of the phases of British history that fascinates the Prime Minister is that of appeasement in the 1930s. After reading Martin Gilbert's study, Descent into Barbarism, last year he asked people in tones of disbelief: did you know that Neville Chamberlain considered a symbolic act of disarmament in order to convince Hitler of our good faith?

There is more, though, to the feebleness of the backlash against Blair than a vague understanding that simply pulling out of Iraq would be no guarantee of being left in peace. There is also the realisation that the Prime Minister was right about the threat. The war might have made it worse, but the threat was real. All those arguments about control orders that raged earlier this year seem to belong to another age. As we catch a glimpse, in the bright lights of hindsight, of the networks of closed terrorist cells of which the security services had only partial knowledge, the idea of special powers beyond the normal standards of proof no longer seems outlandish. Those voices that accused Blair of exaggerating the threat - the equal and opposite of those who accused him of "provoking" the terrorists - have fallen suddenly silent.

This goes beyond the sudden tripartism of tomorrow's meeting between the Home Secretary and his Conservative and Liberal Democrat opposite numbers. It goes back to Blair's motives for joining the Iraq war in the first place. The struggle against al-Qa'ida is "a new type of war", as he said in Sedgefield in March last year. "It forces us to act even when so many comforts seem unaffected, and the threat so far off, if not illusory." Now, the criticism is not that the threat was illusory, but that we could have tried to make sure that it didn't come here.

That is the implication of what Clare Short and John McDonnell said yesterday. There may yet be more of a backlash against Blair than that, especially if the shadow of terrorism falls longer over his third term. But even the argument of the Usual Suspects deserves to be answered. And the answer is to try to understand the nature of the threat, as Blair sought to do in his speech yesterday. The more we try, the more obvious it is that the jihadist ideology did not spring up in response to the Iraq war. It is well established across the Middle East and has long had filaments spreading throughout most of the rest of the world, including here.

The London bombings were not a one-off; the bombers were not isolated, maladjusted individuals. They were psychologically unusual people motivated by a cult-like belief system. No comparison is exact, but they were like the Red Army Faction, animated by what Blair might call a perverted form of Marxism. Or like Timothy McVeigh, animated by anti-government survivalism. Or like the Tamil Tigers, who also use suicide, in what might otherwise be a "conventional" war of national separatism.

The London bombers drew on a similarly potent source. The Pew Global Attitudes survey published last week made sober reading. In Jordan, 57 per cent of the population, many of them Palestinians, say suicide bombings are "sometimes" justified. In Pakistan, 51 per cent have confidence in Osama bin Laden to "do the right thing regarding world affairs".

It is neither tasteful nor accurate to say that the London bombs have revived Blair's fortunes. But he deserves credit for having understood, within moments of the planes hitting the towers in New York, the nature of the threat we faced. Whether or not one thinks his policy on Iraq made it worse or might, in the end, help to reduce it, he took the threat seriously. The failure of an "Iraq backlash" to materialise suggests that most people think that is what their Prime Minister is supposed to do.