We can't go back in; such a move would be unpalatable to most Americans and Iraqis.

From The Washington Post:

Despite a recent U.S. focus on tension between Arabs and Kurds in northern Iraq, Wednesday's strikes [in Baghdad] suggest that the sectarian fight between Shiites and Sunnis over dominance of the country remains far from over.

U.S. military officials in Baghdad said there is little they can do in response to the surge in violence other than pressure Iraqi Prime Minister Nouri al-Maliki to be more cautious as his government takes control of the country's security. Senior American officials have criticized Maliki for recent decisions that they consider overconfident and impulsive. Since the June 30 urban drawdown, his government has sharply restrained the mobility and authority of U.S. troops and his security forces have begun removing blast walls along major roads, declaring the capital safe.

Retired Col. Peter Mansoor, a senior adviser to the top American commander in Iraq in 2007 and 2008, said the Iraqi government is unlikely to ask the U.S. military to reestablish its presence in Baghdad.

"Regrettably, I think we can't go back in," he said, adding that such a move would in any event be unpalatable to most Americans and Iraqis. "The Iraqi government got ahead of itself. It is declaring the war over when it is far from over."

His comments echoed those of other U.S. military officials, who say the United States has reached a point of diminishing returns in its ability to influence Iraqi decisions.