Descent into hell.

The U.S. Institute of Peace's predictions:

1. “The Long Shot to Overcome Ethnic and Sectarian Politics” (most optimistic scenario): “This is an Iraq that slowly, in fits and starts, trudges down the difficult road of creating a functioning state.”

2. “Lebanonization” (militias wage a civil war in the capital): “Unable to maintain control, the United States is itself a target when it becomes involved. … U.S. troops largely retreat behind fortifications, distant from population centers, and head north to Kurdistan.”

3. “Descent Into Hell” (worst-case scenario): Most of Iraq’s neighbors are drawn into open regional warfare, and it ends with Iran conducting strikes against Saudi Arabia’s oil industry.