The United States’ involvement in Iraq just keeps getting messier every day. The insurgency is as potent as ever, and U.S. troops and Iraqi civilians are dying at a higher rate than they were a year ago. Efforts to reconcile Iraq’s ethnic and religious divisions have failed, and progress on building competent security forces has been painfully slow. A series of supposedly decisive “turning points” have come and gone—including the transfer of sovereignty in June 2004, national elections in January 2005, and the drafting of a new constitution in August 2005—but the country is no closer to stability. Public support for the war is plummeting in the United States, and current U.S. troop levels cannot be sustained without breaking the Army, the Reserves, and the National Guard. Once U.S. forces withdraw, a full-blown civil war is likely. Although our armed forces have fought with dedication and courage, this war will ultimately cost us more than $1 trillion, not to mention thousands of lives. And what will the United States have achieved? Remarkably, we will probably leave Iraq in even worse shape than it was under Saddam Hussein.

“Victory has a hundred fathers, but defeat is an orphan.” Those famous words penned long ago have a special resonance today. If the United States loses the war in Iraq, there will inevitably be a bitter debate over who is responsible. With prospects for victory fading, the people who led us into this bastard conflict are already devising various rationales to explain the failure and deny their paternity. As the debate over “who’s losing Iraq” heats up, the American people should not be hoodwinked by these after-the-fact alibis. The architects of defeat must be held responsible.

Moderates who backed the war, including a number of prominent Democrats, now argue...