What Mr. Obama ended was the United States military presence in Iraq, but the fighting did not stop when the last troops left in 2011; it simply stopped being a daily concern for most Americans. While attention shifted elsewhere, the war raged on and has now escalated to its most violent phase since the depths of the occupation.

The turn of events in a country that once dominated the American agenda underscores the approach of a president determined to keep the United States out of what he sees as the quagmires of the last decade. In places like Afghanistan, Egypt, Libya and Syria, Mr. Obama has opted for selective engagement and accepted that sometimes there will be bad results, but in his view not as bad as if the United States immersed itself more assertively in other people’s problems…

Douglas Ollivant, a former national security aide to both Mr. Bush and Mr. Obama, said the administration could not have pushed Mr. Maliki to do more, while the Iraqi leader is “getting a bad rap” since he faces an active Qaeda insurgency. “At least they’re not fighting over us,” Mr. Ollivant said, now that the American presence is no longer an issue.

The strife in Iraq today has turned into part of a larger regional battlefield tied to the civil war next door in Syria. In recent months, American officials said, as many as 50 suicide bombers a month have slipped over the border into Iraq, greatly complicating the nature of the conflict. The Qaeda assaults in Falluja and Ramadi came after a year in which 7,800 civilians and 1,000 Iraqi security troops were killed in attacks, according to the United Nations, the highest levels in five years.