Thanks to oil, Venezuela was once the wealthiest country in the region — before becoming the continent’s poorest, ravaged by corruption and feckless economic policy. And amid the economic decline, high-ranking government officials became conspicuously wealthy. But how? According to U.S. indictments, former government officials, and regional experts, officials linked to the Iran-backed militant group Hezbollah and members of Maduro’s government built a massive drug syndicate — while most of the country increasingly struggled to find food to eat, or medicine to care for the sick. “Venezuela was a narco state several years ago, but it has become darker and...