BAGHDAD - Suspected Sunni insurgents penetrated the Baghdad security net Wednesday, hitting Shiite targets with four bomb attacks that killed 183 people — the bloodiest day since the U.S. troop increase began nine weeks ago. The most devastating blast struck the Sadriyah market as workers were leaving for the day, charring a lineup of minibuses that came to pick them up. At least 127 people were killed and 148 wounded, including men who were rebuilding the market after a Feb. 3 bombing left 137 dead. Wednesday's car bombing appeared meticulously planned. It took place at a pedestrian entrance where tall...