The U.S. mission in Iraq has now lasted longer than America’s involvement in World War II. That should be an occasion for sober reflection. In less than four years — from 1941 to 1945 — the United States and its allies managed to defeat two of the most powerful militaries in the world. By contrast, today, we are still mired in an endless conflict in a single small country after the same amount of time. Those who helped get America into the Iraq quagmire denounce any proposal for withdrawal as “cut and run.” Now that we have passed the World War II milestone, we must demand that the hawks be specific about their strategy. Vacuous statements such as “we will stand down when the Iraqis can stand up” or “we must stay until the job is done” will not suffice.

Except when the survival of the nation is at stake, all military missions must be judged according to a cost-benefit calculation. Iraq has never come close to being a war for America’s survival. It was an elective war — a war of choice, and a bad choice at that. How much are Americans willing to pay in blood, treasure and toil to try to prevail in Iraq?

The costs have already been staggering. We have spent more than $340 billion, and the meter is running at more than $7 billion a month. The loss of life is even more horrific. Nearly 2,900 American troops have perished, and the Iraqi government estimates that 150,000 of its citizens have died in the carnage.

And there is no end in sight. Not only did America’s involvement in World War II last less than four years, it was obvious well before the end that the Axis powers would be utterly defeated. In Iraq, the security environment is worse today than it was when the U.S. occupation began in the spring of 2003. The Sunni-led insurgency against U.S. forces is now merely one component of an increasingly chaotic situation. The upsurge in sectarian violence is an even larger problem, and it has undeniably embroiled the country in a civil war.

The American people need to ask the Bush administration and its hawkish supporters at what point they will admit that the costs have become unbearable. How much longer are they willing to have our troops stay in Iraq? Two years? Five years? Ten years? How many more tax dollars are they willing to pour into Iraq? Another $100 billion? $300 billion? $1 trillion? And most crucial of all, how many more American lives are they willing to sacrifice? One thousand? Five thousand? Ten thousand?

Proponents of the mission studiously avoid addressing such unpleasant questions. They act as though victory in Iraq can be achieved merely through the exercise of willpower. President Bush epitomized that attitude during his recent trip to East Asia, when he asserted that the United States would definitely win in Iraq — unless we decided to quit before the job was done.

That is a dangerous delusion. Victory is by no means guaranteed, no matter what effort the United States makes. Iraq is a fractious place that may not prove even to be a viable country. America’s credibility in the world will take a hit if we withdraw our forces and admit that the mission has failed. That should be a sobering lesson not to undertake impractical nation-building ventures in the first place. But a withdrawal now will be less painful than a withdrawal years from now, after we have incurred far greater losses in lives and money.

It is better to bite the bullet and start to pull our troops out today. Otherwise, we may still be having the same debate in 2013 — when our involvement in Iraq will surpass the length of our war in Vietnam. That is a milestone no one should want to pass.