Mr. Maliki is reputed to be canny, but his better instincts abandoned him here. A savvy politician gives himself an escape hatch, just in case. For the sake of Iraq and the combustible Persian Gulf region, the Prime Minister and the Obama Administration should find a way to walk back from his intemperate demarche.

The Prime Minister was no doubt playing the nationalism card for his domestic audience, and we can understand the impulse to send Americans home after the long fight for liberation from Saddam and al Qaeda. He may also think that America's departure will mark a coming of age for the new Iraq.

Progress has been undeniable—the too little reported good news story of 2010. This year saw the lowest number of civilian casualties since the 2003 invasion, and terrorism no longer poses a mortal threat to the state. The coalition formed after a close election in March has also brought Sunnis, Shiites and Kurds under the same tent. The economy is booming. Fewer than 50,000 American troops are left, based outside the cities and no longer engaged in combat. By the terms of the current status of forces agreement, all will leave within 12 months.

Iraq's own 700,000-strong security forces have matured to the challenge of keeping peace in the country. But the U.S. military now plays a different role as a guarantor of stability in Iraq and the neighborhood. The sectarian groups still compete fiercely over the division of spoils and power. Iraqis know that America has no designs on Iraq territory or resources, which is why it is trusted as an honest broker.

Iraq's north around Mosul is a particular sore point. Sunnis, Kurds and smaller ethnic groups are facing off over control of oil resources below Kurdistan. Nearly 10,000 U.S. troops, a fifth of the remaining force, help keep the peace in the province of Neneveh, manning checkpoints, while U.S. officials help work out a political solution. The disputes are unlikely to be solved in a year.

Sunni terrorist groups are busy exploiting the existing tensions. The Iraqi police commander in Mosul was killed Wednesday in a multiple suicide bomb attack on his headquarters. Shamel Ahmed Ugla, the commander, had led the fight on al Qaeda in Iraq in the region.

The formation of a unified government showed the resilience of Iraq's political system, but the nine months of infighting leading up to it were a reminder of its fragility. The presence of the anti-American Shiite cleric Moqtada al-Sadr's party in the coalition makes Sunnis nervous. At least the Sadr group has no say over security forces. Mr. Maliki's political rivals think the Prime Minister harbors an authoritarian streak and enjoys too much control over a Shiite-dominated military. U.S. forces would have an especially reassuring effect on the Kurds, a long-suffering minority that doesn't trust Baghdad.

The presence of U.S. forces in Iraq can also have a stabilizing impact in the region, much as U.S. troops in Japan and South Korea have had in Asia nearly 60 years after the end of the Korean War. The U.S. can help to shield Iraq from undue Saudi or Iranian pressure with troops on the ground, while making Iran think twice about regional adventures. With the right atmospherics and conditions, this insurance policy need not be controversial in the U.S. or Iraq.

The Obama Administration has known the 2011 deadline was coming, and it's a blunder not to have been quietly negotiating with Mr. Maliki for a new forces agreement. Little time remains to sort out a compromise or get a new deal. The U.S. military doesn't travel light, and it needs to know as soon as possible if troops are to stay in Iraq. We hope Mr. Maliki's comments this week haven't shut the door on a partnership that would benefit both countries.