MEXICO CITY — If there had been odds on which Mexican politician was colluding with the cartels, the favorite might have been Rubén Rocha Moya. Rocha, the governor of Sinaloa, has long been dogged by accusations of protecting his state’s dominant criminal organization, the Sinaloa Cartel, a prolific supplier of fentanyl and ruthless purveyor of violence. Those accusations reached a fever pitch in 2024 when the U.S. authorities arrested the cartel’s co-founder, who then said he thought he had been on his way to meet Rocha. Yet, instead of investigating, Mexico’s leaders rushed to Rocha’s defense. The president at the time, Andrés Manuel López Obrador, and president-elect, Claudia Sheinbaum, quickly joined hands with Rocha on a stage in Sinaloa. “I came to pledge to continue fighting alongside you,” Sheinbaum said. That promise just got a lot more complicated. On Wednesday, U.S. prosecutors unsealed an indictment that put teeth behind the years of accusations against Rocha.…