Seldom has an image so clearly marked the turning of the world. One of man’s mightiest structures collapses into an immense white blossom of churning, roiling dust, metamorphosing in 14 seconds from hundred-story giant of the earth into towering white plume reaching to heaven. The demise of the World Trade Center gave Americans an image as newborn to the world as the mushroom cloud must have appeared to those who first cast eyes on it.



In the face of the unimaginable, small wonder that leaders would revert to the language of apocalypse, of crusade, of “moral clarity.” Speaking at the National Cathedral just three days after the attacks, President George W. Bush declared that Americans’ “responsibility to history is already clear: to answer these attacks and rid the world of evil.” Astonishing words - imaginable, perhaps, only from an American president, leading a people given naturally in times of crisis to enlisting national power in the cause of universal redemption.

A withdrawal from Iraq, rapid or slow, with the Islamists still holding the field, will signal a failure of American will.

Four years after the collapse of the towers, evil is still with us and so is terrorism.



Terrorists have staged spectacular attacks, killing thousands, in Tunisia, Bali, Mombasa, Riyadh, Istanbul, Casablanca, Jakarta, Madrid, Sharm el Sheik and London, to name only the best known.



Last year, they mounted 651 “significant terrorist attacks,” triple the number from the year before and the highest since the State Department started gathering figures two decades ago. One hundred ninety-eight of these came in Iraq, Bush’s “central front of the war on terror” - nine times the number of the year before.



Al Qaeda, according to the president, has been severely wounded.



“We’ve captured or killed two-thirds of their known leaders,” he said last year. And yet however degraded Al Qaeda’s operational capacity, nearly every other month, it seems, Osama bin Laden or one of his henchmen appears on the world’s television screens to expatiate on the ideology and strategy of global jihad and to urge followers on to more audacious and more lethal efforts.



This, and the sheer number and breadth of terrorist attacks, suggest strongly that Al Qaeda has become Al Qaedaism - that under the American and allied assault, what had been a relatively small, conspiratorial organization has mutated into a worldwide political movement, with thousands of followers eager to adopt its methods and advance its aims.



Call it viral Al Qaeda, carried by strongly motivated next-generation followers who download from the Internet’s virtual training camp their tradecraft in terror.



Americans have managed to show themselves, their friends and most of all their enemies the limits of American power.



And they are fighting - as the escalating numbers of terrorist attacks, the grinding Iraq insurgency, the overstretched American military and the increasing political dissatisfaction at home show - precisely the kind of war Al Qaeda wanted them to fight.



The 9/11 attacks seem to have been intended at least in part to provoke an overwhelming American response: most likely an invasion of Afghanistan, which would lead the United States, like the Soviet Union before it, into an endless, costly and politically fatal quagmire.



For the jihadists, luring the Americans into Afghanistan would accomplish at least two things: By drawing the United States into a protracted guerrilla war in which the superpower would occupy a Muslim country and kill Muslim civilians - with the world media, including independent Arab networks like Al Jazeera, broadcasting the carnage - it would leave increasingly isolated those autocratic Muslim regimes that depended for their survival on American support.



And by forcing the United States to prosecute a long, costly and inconclusive guerrilla war, it would severely test, and ultimately break, American will, leading to a collapse of American prestige and an eventual withdrawal - first, physically, from Afghanistan and then, politically, from the “apostate regimes” in Riyadh, Cairo and elsewhere in the Islamic world.



In Afghanistan, bin Laden would be disappointed. The U.S. military initially sent in no heavy armor but instead restricted the American effort to aerial bombardment in support of several hundred Special Operations soldiers on the ground who helped lead the Northern Alliance forces in a rapid advance. Kabul and other cities quickly fell. America was caught in no Afghan quagmire, or at least not in the sort of protracted, highly televisual bloody mess that bin Laden had envisioned.



But bin Laden and his senior leadership, holed up in the mountain complex of Tora Bora, managed to survive the bombing and elude the Afghan forces that the Americans commissioned to capture them. During the next months and years, as the United States and its allies did great damage to Al Qaeda’s operational cadre, arresting or killing thousands of its veterans, its major leadership symbols survived intact, and those symbols, and their power to lead and to inspire, became Al Qaeda’s most important asset.



We cannot know what future Osama bin Laden imagined when he sent off his 19 suicide terrorists on their mission four years ago. He was wrong about Afghanistan, and there has been no uprising in the Islamic world.



One suspects, though, that if he had been told on that day that in a mere 48 months he would behold a world in which the United States, “the idol of the age,” would be bogged down in an endless guerrilla war, fighting in a major Muslim country; a world in which its all-powerful army, with few allies and little sympathy, would find itself overstretched and exhausted; in which its dispirited people would start to demand from their increasingly unpopular leader a withdrawal without victory - one suspects that such a prophecy would have pleased him.



Bin Laden has suffered damage as well. Many of his closest collaborators have been killed or captured, his training camps destroyed, his sanctuary occupied. But Al Qaeda was always a flexible, ghostly organization, a complex worldwide network of shifting alliances and marriages of convenience with other shadowy groups. Now Al Qaeda’s “center of gravity,” such as it is, has gone elsewhere.



What seems most notable about the Madrid attack - and the attack on Jewish and foreign sites in Casablanca on May 17, 2003, among others - is that the perpetrators were “home-grown” and not, strictly speaking, Al Qaeda.



“After 2001, when the U.S. destroyed the camps and housing and turned off the funding, bin Laden was left with little control,” Marc Sageman, a psychiatrist and former CIA case officer who has studied the structure of the network, has written. “The movement has now degenerated into something like the Internet. Spontaneous groups of friends, as in Madrid and Casablanca, who have few links to any central leadership, are generating sometimes very dangerous terrorist operations, notwithstanding their frequent errors and poor training.”



We have entered the era of the amateurs.



In starting a war in Iraq that they have been unable to win, Americans have done the one thing a leader is supposed never to do: issue a command that is not followed.



A withdrawal from Iraq, rapid or slow, with the Islamists still holding the field, will signal, as bin Laden anticipated, a failure of American will.



Those who will view such a withdrawal as the critical first step in a broader retreat from the Middle East will surely be encouraged to go on the attack. That is, after all, what you do when your enemy retreats. In this new world, where what is necessary to go on the attack is not armies or training or even technology but desire and political will, America has ensured, by the way it has fought this forever war, that it is precisely these qualities its enemies have in large and growing supply.



This was excerpted from an article in The New York Times Magazine. Mark Danner is the author of “Torture and Truth: America, Abu Ghraib and the War on Terror.”