SLIDELL, La. — It was just before dawn when the pickup truck arrived at the two-story house in this middle-class suburb, which was hit hard by Hurricane Katrina. But unlike most of the trucks here now, it was not carrying construction supplies. Federal agents, who were hiding in the bushes, say the truck was bringing 50 kilograms of cocaine, worth $5 million, from Houston to the murderous streets of nearby New Orleans. They also say that the shipment, seized on May 18, was at least five times as large as the typical drug delivery before the storm. The drug trade...