SEOUL—Just a year ago, South Korean President Moon Jae-in’s left-leaning Democratic Party was riding high. It had just won a historic three-fifths majority in the country’s legislature. Voters rewarded the administration’s handling of the pandemic.
But now, South Korea’s conservatives are making a comeback. With the final votes tallied on Thursday, candidates from the right-leaning People Power Party easily won mayoral races in the country’s two-largest cities, steamrolling opponents from Mr. Moon’s ruling party. It wasn’t close: the margin of victory eclipsed 18 percentage points in Seoul, while it hit nearly 30 percentage points in Busan.
Mr. Moon, who took office in 2017 for a five-year term, called the pair of defeats a reprimand from voters. “We will approach our work with more humility and a deeper sense of responsibility,” said Mr. Moon, through a presidential spokesman.
The final race outcomes provide a snapshot of…