CIUDAD JUAREZ, Mexico—Magda Rubio had just launched her campaign for mayor of a small city in northern Mexico, when a chilling voice came through her cell phone. “Drop out,” the caller warned, “or be killed.”
It was the first of four death threats Rubio said she has received since January from the same well-spoken, anonymous man. She has stayed in the race in Guachochi, located in a mountainous region of Chihuahua state that is a key route for heroin trafficking. But two armed bodyguards now follow her round the clock.
