The United States has diplomatic relations with 194 independent nations. Of these, none is more important to America than Mexico in terms of trade, investment, tourism, natural resources, migration, energy, and security. In recent years, narco-violence has afflicted our neighbor to the south-with more than 50,000 drug-related murders since 2007 and some 26,000 men, women, and children missing. President Enrique Pena Nieto has tried to divert national attention from the bloodshed through reforms in energy, education, anti-hunger, health care, and other areas. Even though the death rate has...