This will be a big year for Mexico, with a presidential election in July. Legendary leftist Andrés Manuel López Obrador is running as the anticorruption candidate. It’s the 64-year-old’s third run for president, and this time he’s framing himself as a crusader against what he calls a rigged system.

Mexico is an increasingly urban nation with a rising middle class that has widely benefited from economic modernization over the past three decades. Mr. López Obrador has spent a political lifetime fighting this change. From deregulation...