The agreement finalized that day was the last real power-sharing accord Iraq had, and it failed almost immediately. Thanks to Maliki and his opponents' intransigence, the deal was never implemented and the country's sectarian divides widened. Maliki has governed more as a defender of the Shiites than as an inclusive national leader.

Now, as violent Sunni militants from the Islamic State of Iraq and Syria (ISIS) cement their hold over western Iraq, declare a caliphate, and threaten a new civil war, Washington has again demanded that Iraq's leaders form an inclusive government encompassing the country's minority Sunnis and Kurds.

But former officials and even some in the current Obama administration say that effort may also founder. Maliki had been expected to be named prime minister for a third term after his coalition won April elections, but as security deteriorates pressure is mounting even from within his Shiite power base for him to go. Even if he is pushed aside, Washington will likely struggle to exert much sway over the situation.

More than a dozen former and current diplomats say the relationship between Washington and Baghdad has been marred by repeated missteps by both Obama and his predecessor, President George W. Bush. Washington, the diplomats say, has been unwilling or unable to influence Iraqi politicians and in particular the man they helped bring to power.

While Maliki lost the 2010 elections, he emerged stronger, said Emma Sky, a British Middle East scholar who was a political adviser to U.S. General Raymond Odierno from 2007 to 2010. Maliki then "faced no consequences when he reneged on his commitments" to integrate Sunnis into the government, she said.

Ali Khedery, a long-serving adviser to multiple U.S. ambassadors in Baghdad, said he resigned after warning in an October 2010 memorandum that U.S. backing for Maliki's premiership would lead to dictatorship, renewed civil war, and Iranian hegemony in Iraq. Other U.S. and British officials who shared his view had left Baghdad by the fall of 2010, he said, but his memo reached top White House officials, who overruled him.

To be fair, Maliki took some early positive steps, including facilitating the U.S. surge and confronting Shiite militiamen in Basra, according to former U.S. ambassador to Baghdad Zalmay Khalilzad. But his rule has proved increasingly divisive.

Maliki's office declined to comment for this story, citing the demands on his time from the war campaign and efforts to choose a new government. Maliki has long blamed his opponents for sabotaging him, and feels let down by Washington.

"There is a bitterness in Maliki's tone when he talks ... about the American role, even what is going on in D.C., with speeches in Congress and Obama's speech," longtime Maliki ally Sami Askari said about his mood in recent weeks. "He ... has no hope. He says we have to rely on ourselves."