The end of the Iraq war in 2011 was a high point of President Obama's first term, marking the completion of one of his most important campaign promises. But as Islamic militants capture cities and towns throughout Iraq and march toward the capital, Baghdad, the president once again faces the criticism that his foreign policy has failed.
Worse yet, it stands to undermine his foreign policy legacy.
The violence has swept Iraq just two and a half years after the last U.S. troops departed following a nearly nine-year war. The gains made during the war have been wiped out with the rise of the Islamic State of Iraq and Syria (ISIS). The group's advance raises questions that will likely dog the president during the remainder of his time in office, from whether U.S. forces should have stayed behind, to how he might have tried to alter the course of events in recent years, to whether a similar policy in Afghanistan is doomed for failure.
Experts almost entirely agree that Mr. Obama could have done things differently, but differ on the question of how much blame he bears for the situation, when he might have changed course, and even whether it would have substantially changed the situation.
Why Iraq is plagued by violence
CBS News National Security Analyst Juan Zarate, a former Bush administration national security adviser, traces the trouble in part back to 2011, when U.S. troops withdrew from Iraq. Prime Minister Nouri al-Maliki refused to sign an agreement allowing for a residual force to remain behind, but Mr. Obama was also interested in bringing the war to an end, as he promised during the 2008 campaign.
That was a criticism from Sen. John McCain, R-Ariz., who faced off against Mr. Obama in the 2008 election on issues including Iraq policy.
"What the Americans left behind was an Iraqi state that was not able to stand on its own," he said Thursday.
Zarate argues that the lack of an American presence on the ground has limited the U.S. ability to support the Iraqi military and be prepared for an increase in violence.
"This is not America's fault, but we're certainly not in a good posture to deal with the situation and I don't think the administration has put us in a very good position to be able to respond with all options against this threat," he said.
But other experts argue that the U.S. had no choice but to respect Iraq's decision to end the American troop presence.
"Fundamentally the Iraqis asked us to leave and that was their prerogative and their choice," Brookings Institution senior fellow Michael O'Hanlon told CBS News.
Many people have pointed fingers at Maliki, who they say has weakened the Iraqi government and other institutions he controls, like the army. As the head of the Shiite-led government, he has become an increasingly authoritarian figure who has refused to take steps to integrate Iraq's Sunni and Kurdish minorities as the U.S. recommended.
"All the blame, in my view, rests with Maliki," said Michael Morell, the former deputy CIA director who now serves as a security analyst for CBS News. "He would not accept U.S. help, even behind the scenes, until recently, and he didn't keep the pressure on [ISIS]. You have to keep the pressure on the terrorist groups or they rebound quickly."
But Morell still says he's "not sure that had we left behind a small number of troops for training purposes, which is what it was going to be, that we would be a significantly different place now."
There are other theories about how Mr. Obama might have acted differently.