Perhaps the country will hold together long enough for the US's rushed withdrawal, but recent attacks are a gloomy portent

Barack Obama's unannounced flying visit to Baghdad comes at a time of growing concern that hard-won security gains of the past 18 months are beginning to unravel. While he may wish Iraq a safe and prosperous future, the US leader's top priority is plainly an orderly American military withdrawal. Obama has other fish to fry, notably Iran and Pakistan-Afghanistan. Problem is, Iraq is not over.

A string of car bombings in Shia areas of Baghdad this week gave deathly voice to newly rising tensions between Sunni Arab groups and the Shia-led coalition government of prime minister Nouri al-Maliki. The attacks were...