Since the first major outbreak last February, South Korea’s COVID-19 response has been a model for other nations—its government praised for its ability to quash each spike in infections without severe lockdowns, relying instead on quick action, extensive testing and tech-powered contact tracing, along with social distancing and public cooperation. But lately, President Moon Jae-in’s popularity inside the country has been sinking—in part because of frustration over the speed of vaccine rollout.