When Tony Blair, having procrastinated about his departure almost to the point of unreason, finally gives up the British premiership this month, it will be to the general relief not only of the British public as a whole, but also of the overwhelming majority of his own party. After three terms in office, it could hardly be otherwise. Despite the cliché, power does corrupt, and the late Blair era, like that of Margaret Thatcher before it, has been a squalid spectacle.

The paradox is that, for a man who wielded so much power for so long, it is unclear what domestic legacy, if any, Blair will leave. Blairism was a mood, a style, but, in substantive terms, it represented no radical break with the Thatcherite legacy that New Labour repackaged so cleverly, and, in fairness, administered more humanely than the Iron Lady ever did.

Foreign policy is another story. Whatever one thinks of him, in international affairs Blair was a leader of consequence. Indeed, he can be plausibly described as being chiefly responsible for formulating and successfully propagating the doctrine of “humanitarian intervention.” That idea captured the imagination of much of the elite of the developed world over the course of the 1990’s, and provided the moral rationale for the principal Western military interventions of the post-Cold War period, from Bosnia to Iraq.

Given how catastrophic the invasion of Iraq has turned out to be, it is hard even to remember when interventions on moral grounds – whether to thwart a dictator, as in the case of the Balkan wars, or to put an end to anarchic cruelty, as in the case of British intervention in Sierra Leone – seemed like a great advance in international affairs. No longer would the powerful sit by idly while butchers like Slobodan Milosevic or Foday Sankoh slaughtered their own people.

Today, humanitarian intervention has become a dirty word for many of the same people who once believed in it. Only American neo-conservatives, understandably grateful for his championing of the Iraq war and his ability to argue for it coherently and eloquently (unlike President Bush, who was and is unable to do either), are sorry to see Blair go. But what may be lost is how many people did believe.

Blair still does. In a recent interview, he replied to the question of the core of his foreign policy with two words: “liberal interventionism.” The world may have moved on, chastened by the realization that interveners, even when intervening in the name of human rights, can be as barbaric as tin pot dictators. But Blair, it seems, is not to be moved. What was famously said of Thatcher – “the lady’s not for turning” – can be said of him as well.

In fairness to Blair, this is not mere stubbornness, as it seems to the case with Bush and his current and erstwhile minions, Donald Rumsfeld, Paul Wolfowitz, and, of course, Vice President Dick Cheney. For Blair, there is a moral unity between the interventions in Kosovo and Iraq, both of which he presents as examples of a post-Westphalian idea that powerful states are called upon to defend suffering communities globally, including by military means.

To the charge that this idea is actually old-fashioned liberal imperialism updated for the post-Cold War world, Blair has consistently replied that what he called for in Kosovo, Sierra Leone, and Iraq are wars of “values, not interests.” In his more petulant moments, he has asked why so many of those who saw no harm in NATO undermining Milosevic adamantly opposed the ouster of Saddam Hussein.

Actually, the answer is quite simple. Blair’s vision of wars of values rather than interests has increasingly come to seem like a moral flag of convenience – in a way similar to the use of human rights by the rich world’s governments to justify their continued domination of institutions like the World Bank and the IMF. The fact that NATO now considers its area of operations to legitimately extend all the way to the Hindu Kush has given pause even to many who once believed as fervently in humanitarian intervention as Blair still does.

Of course, Blair does not think of himself as a new imperialist. On the contrary, as he has frequently made clear, he considers his critics immoral for not supporting liberal interventions. But nor did nineteenth-century colonialists think of themselves as immoral. Indeed, perhaps the greatest of British imperial conquerors in Africa, Cecil Rhodes, once defined imperialism as “philanthropy plus 5%.” Take that, Dick Cheney and Halliburton.

Doubtless, we will learn more about Blair’s justifications for what he did, and further articulations of his interventionist creed, when he goes on the lecture circuit and, in due course, publishes his memoirs. The pathos of his situation, though, is that no one is listening anymore.

Blair is the last interventionist. Neither his successor, Gordon Brown, nor George W. Bush’s successor, whoever he or she turns out to be, will be able to mount another intervention similar to that in Kosovo, let alone Iraq.

Those pressing for military intervention in Darfur would probably say that this is a bad thing. But, as they rail against the failure of the West to take action, they should remember why such action is impossible. By putting liberal interventionism at the heart of his foreign policy, Tony Blair has made it radioactive – a political non-starter for at least a generation.