Mexico City’s subway system has been plagued with problems for years. On Monday, an overpass collapsed, and the newest subway line plunged some 50 feet, killing at least 24 people and setting off a political firestorm.

Mexico City’s subway system has been plagued with problems for years. On Monday, an overpass collapsed, and the newest subway line plunged some 50 feet, killing at least 24 people and setting off a political firestorm.