In one of the new joint American-Iraqi security stations in the capital this month, in the volatile Ghazaliya neighborhood, Capt. Darren Fowler was heaping praise on his Iraqi counterparts for helping capture three insurgent suspects who had provided information he believed would save American lives. “The detainee gave us names from the highest to the lowest,” Captain Fowler told the Iraqi soldiers. “He showed us their safe houses, where they store weapons and I.E.D.’s and where they keep kidnap victims, how they get weapons, where weapons come from, how they place I.E.D.’s, attack us and go away. Because you detained...