Mexican President Andrés Manuel López Obrador imposed a 50 percent tariff on white corn imports largely coming from the U.S. The rationale being provided is that it is to protect the country’s historical and indigenous corn varieties. Eso es una tonteria. Mexicans eat white corn and the overwhelming variety that is being produced and eaten in Mexico are hybrids. So-called heirloom varieties comprise less than one percent of Mexico’s corn production. Notably, heirloom production is increasing but that is not due to Mexicans but increased exports to fulfill gowing demand in rich countries. Heirloom corn costs three times as much and is therefore not the source of the daily tortilla for most Mexicans. AMLO is playing...