The Drop in Crime in El Salvador Is Stunning, but It Has a Dark Side

Voters in El Salvador this week gave their tough-on-crime president a sweeping mandate: Keep going.

While votes are still being counted, President Nayib Bukele claims he won re-election by a landslide, with more than 85 percent of the vote. If those results hold when the official count is announced, not even Latin America’s best-known populist presidents, like Venezuela’s Hugo Chávez or Bolivia’s Evo Morales, will have come close to winning election by such margins.

Mr. Bukele’s unparalleled rise comes down to a single factor: El Salvador’s stunning crime drop. Since he took office in...