“What’s the difference between Iraq and Afghanistan?” asked John Noonan, a top House Armed Services Committee Republican aide, on Twitter last week. “A: About 5 years.”

No one in Washington is laughing.

Instead, worry is quietly building that the ongoing crisis in Iraq — the struggles of a government partly seen as illegitimate, the collapse of its American-trained military and the ascendance of Islamic extremists — is just Part 1 of a grim coda to George W. Bush’s foreign policy.