Municipal and federal police officers confront each other in Monterrey, Mexico, this summer after federal authorities arrested dozens of officers from several towns who were accused of colluding with drug traffickers. (Christian Lara / Grupo Reforma) At the heart of the overhaul is a "new police model" that stresses technical sophistication and trustworthiness and that treats police work as a professional career, not a fallback job. In steps that are groundbreaking for Mexico, cadets and...