MEXICO CITY (AP) — With Sinaloa cartel boss Joaquín “El Chapo” Guzmán serving a life sentence, his sons steered the family business into fentanyl, establishing a network of labs churning out massive quantities of the cheap, deadly drug that they smuggled into the U.S., prosecutors revealed in a recent indictment. Although Guzmán’s trial revolved around cocaine shipments, the case against his sons exposes the inner workings of a cartel undergoing a generational shift as it worked “to manufacture the most potent fentanyl and to sell it in the United States at the lowest price,” according to the indictment unsealed April...