BAGHDAD — A bomb in a sprawling Shiite Muslim neighborhood of Baghdad killed at least 72 people and wounded more than 135 Wednesday, highlighting the danger that Iraq will slip back into violence after a deadline for U.S. combat troops to leave its cities — now less than a week away. It was unclear who was responsible for the bomb, which was hidden in a motorcycle with a vegetable cart attached. Some blamed Sunni insurgents from Al Qaeda in Iraq or remnants of Saddam Hussein’s Baath Party, but others raised the possibility that the bombing was the result of disputes among Shiite factions. In either case, such bloodshed represented a major challenge for Prime Minister Nouri Maliki. Maliki, a Shiite, has asserted that Iraqi forces are ready to take on responsibility for security with limited help from the U.S. military. His government has declared June 30, the deadline for U.S. troops to pull back from Iraq’s cities, a national holiday. Maliki has acknowledged there will be attacks in the days ahead, but insists Iraqi forces are up to the task. Last week, the senior U.S. military commander in Iraq, Gen. Ray Odierno, expressed confidence in the Iraqi […]