David Schanzer is director of the Triangle Center on Terrorism and Homeland Security at Duke University and UNC-Chapel Hill.

It is tempting to agree with those who argue that our departure from Iraq is necessary to change the political dynamic in that country and to relieve the burden of war on our nation. But our deep interests in averting a regional crisis, preventing al-Qaeda and other Islamist radicals from gaining sanctuary in central Iraq and fulfilling our moral responsibility to the Iraqi people lead me to conclude that we should make one more effort to salvage this tragically mistaken conflict.

The security measures and regional diplomacy recommended by the Iraq Study Group will not bring about meaningful progress without a political agreement between parties representing broad majorities of Shia and Sunni Iraqis. Such an agreement must include compromises over the powers of Iraq's national government, regionalization, division of oil revenues, decommissioning of militias, amnesty, the status of former Baath Party members, and revisions to Iraq's constitution. We have been trying unsuccessfully to forge such a compromise for over two years. Now, there are very few cards left to play.

Our only leverage is to present a stark choice to the Shia and Sunnis: either reconcile your differences now, in which case America will remain your partner and provide the resources and assistance necessary to build a stable government, or you are on your own. Only this blunt threat, which has only recently become credible due to the November elections and the Iraq Study Group report, might result in the Iraqis moving away from the abyss and toward some form of nationhood.

Without an agreement, there is no Iraq. Our current goal of creating a stable government that can defend itself, therefore, would be unachievable. Our troops would have no mission other than the untenable prospect of refereeing a full scale civil war and overseeing the breakup of Iraq. Many believe this is already happening and there is nothing we can do to prevent it. They may be right.

Nonetheless, even if the odds are stacked heavily against us, the consequences are so severe that we need to make one last ditch effort to avoid the violent disintegration of a country that we invaded.

Even if the parties can begin to achieve national reconciliation, the road ahead would be fraught with peril. A large-scale American military presence will be necessary for a prolonged period to enforce the political settlement and build all the security forces into national, nonsectarian institutions. Progress will be halting, with many setbacks and spasms of violence. But this would be far superior to chaos, escalating violence, a humanitarian crisis, reduced oil supplies, an emboldened and empowered Iran and other repercussions throughout the Middle East.

The American people must understand that no matter which path is taken, the Iraq debacle will cause serious problems for many years to come, require the expenditure of many billions of taxpayer dollars, preoccupy our government and drag down our international prestige and power. There is no "victory" to be had -- we are now in the phase of managing the consequences of a failed policy.

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