An opposition party has won the mayoral race in Istanbul, Turkey’s largest city, opening up longtime president Recep Tayyip Erdogan to a stinging defeat. The opposition-party candidate won 54 percent of the vote, with nearly all votes counted. The tally prompted his opponent—President Erdogan’s chosen candidate—to concede. Erdogan has previously said that “whoever wins Istanbul, wins Turkey.” Erdogan began his political career as Istanbul’s mayor. The opposition’s win would be the biggest defeat of Erdogan’s political career, ending his party’s 25-year dominance of the city, and could likely spell the end of his 16-year rule over Turkey.