In Iraq, they say, failure is not an option. But it is a possibility.

From the start of the intervention, two critical questions have awaited answers: Is there a critical mass of Iraqis who are willing to fight for freedom rather than submit to tyranny? And can the American military – designed to confront the Soviet Union, a lumbering giant – learn to effectively fight an elusive enemy who plays by no rules and need not win a single battle? All that the enemy has to do is erode our will to fight. Videotapes of beheadings and suicide bombings tend to have that effect on the Western psyche.

More than two years into the war, those who insist Iraq is a hopeless quagmire can point out that, in recent weeks, 130 car bombs have left more than 600 people dead.

On the other hand, thousands of freshly trained Iraqi troops have begun hunting insurgents in and around Baghdad. Even in the most restive provinces of the country, Sunni tribesmen have been battling the forces of Abu Musab al-Zarqawi, leader of al-Qaeda in Iraq. And Zarqawi himself is reportedly wounded.

But leave aside, for the moment, the question of whether we are today inching forward or slipping back. Focus instead on this: Has failure now become an option? What would be the consequence of an American defeat in Iraq?

It surely would mean a bloodbath as the Ba’athist insurgents and al Qaeda terrorists settled scores and demonstrated _ as an object lesson for others _ the price that must be paid for collaborating with American infidels.

Iraqi terrorist training camps would no doubt be reopened. Refurbishing Salman Pak, for example, not only would humiliate America but, more practically, could turn out skilled replacements for those combatants lost during the Iraq and Afghanistan campaigns.

On a conceptual level, it would now be apparent that America’s flight from Beirut after the slaughter of its Marines in 1983, its hasty withdrawal from Somalia 10 years later, its refusal to hold any terrorist nation, dictator or group responsible for the first World Trade Center bombing _ these were not flukes or mistakes but points in a trend line. It would confirm the belief that the West is in decline and that a superior force is destined to prevail _ exactly what both Osama bin Laden and Saddam Hussein have long predicted.

Al Qaeda, Saddam loyalists, agents of the Iranian mullahs _ whichever group or alliance of groups emerged on top in Iraq would build on their success. Before long we could expect an “insurgency” in Kuwait: the assassination of a few key figures, some beheadings and suicide bombings. The wave would continue into Jordan, Saudi Arabia, Egypt, Pakistan and beyond. Who would stop it? How would they stop it?

With expanding territory, population and resources, including vast oil wealth, the leaders of the new totalitarian confederation or empire _ or caliphate _ could manipulate the world’s economy to its benefit and to the detriment of those few nations who might dare obstruct their ascendance. Nuclear, biological and chemical weapons would soon be theirs. They’d want them only for peaceful purposes, of course; and for deterrence.

Before long, the dream of both Saddam and bin Laden would be realized. There would be an oil-rich, nuclear-armed new superpower, a true rival to the decadent and divided West. Quietly, it would empower “non-state actors,” AKA, terrorist groups.

In Europe, radical Islamists would become increasingly demanding. They’d find European leaders surprisingly accommodating. Americans, by contrast, would be obstreperous and try to better seal their borders. Such efforts would only delay the inevitable. Chances are that, eventually, a nuclear weapon or germ bomb would be detonated in some American population center. World leaders would express sympathy. But what could be done? Investigate who had supplied it to whom? Ask the United Nations to impose sanctions? Retaliate against the civilian populations of Baghdad and Tehran?

That war is hell is not news. That the war in Iraq is more hellish than many imagined is obvious. It is legitimate, indeed useful, to criticize the Bush administration’s conduct of the war. But those who interpret every helicopter crash, bombing or decapitation as proof that America’s 21st century enemies can’t be beaten, those who urge _ or merely imply _ that the U.S. should accept defeat, need to say what they expect would happen after U.S. forces went home.

Will it be anything like the apocalyptic scenario sketched above? If not, why not?

Some people may answer by saying that after the U.S. defeat in Vietnam life returned to normal for most Americans. But Ho Chi Min had modest ambitions. He never sought to topple the American colossus; the Viet Cong never attempted to massacre Americans on American soil.

This enemy is different. This war is different. This time, America has to win. Failure is not an option.

Clifford D. May is president of the Foundation for the Defense of Democracies, a policy institute focusing on terrorism.