Mexico today increasingly resembles Colombia 25 years ago. Drug cartels are strengthening rapidly, Mexico's governmental authority and legitimacy are weakening and the people are deeply divided over how to respond to the cartels' challenge to Mexico's civil society. The stakes for the United States were high in Colombia back then, but they are even higher now in Mexico. The drug cartel threat has already rendered broad areas on our side of the border unsafe. The State Department has ordered dependents in some consular posts to leave Mexico and warned against cross-border travel by land, even in daylight. Central American diplomats...