Ekrem Imamoglu, the mayor of Istanbul and a popular figure, had boasted jokingly that he was the only person to have beaten Recep Tayyip Erdogan’s ruling party in three local elections.

Ivan Hansen, a retired Danish police officer, loaded up his basket at the supermarket, carefully checking each product to avoid buying anything made in the United States. The 67-year-old said it's the only way he knows to protest U.S. President Donald Trump's policies.

Turkey’s next presidential election is in 2028, so why would the mayor of Istanbul, a Recep Tayyip Erdoğan rival, be arrested now? One reason: The autocratic Mr. Erdoğan fears a loosening hold on voters.