In the immediate aftermath of the attack in Oslo, speculation about the party that might be responsible has centered on Ansar al-Islam, a Kurdish militant group that has been tied by U.S. officials to al-Qaeda and that carried out attacks on American troops and civilians in Iraq at the height of the war there. Norway’s contingent in Afghanistan, or even its “cartoon crisis” of 2006, could make the country a target for any number of terrorist groups, as the Atlantic has noted. Already, there’s been at least one claim of responsibility for Friday’s bombing from an al-Qaeda-linked jihadist. The U.S....