But the improvements in Iraq face an array of destabilizing provincial, national and regional forces. The Sunni insurgency — now in many places operating as pro-American Awakening groups — continues to wait to see whether the government makes good on promises of jobs and a less sectarian administration of security and public services and infrastructure.

The Sadrists remain powerful and may not forgive what many consider a betrayal by Mr. Maliki, who could not have become prime minister two years ago without their blessing. Mohanned al-Gharrawi, a senior Sadrist cleric in Baghdad, said, “We feel like a bridge that they used to reach their aims and goals, and then they left us behind.”

Despite their newfound confidence, some senior Iraqi officials close to Mr. Maliki said that without an American military safety net they are vulnerable to threats from outside and inside their borders.