For years, Turkey was the model of progress for many Muslim countries. But the military’s retreat has been driven, in part, by the country’s desire to join the European Union. And the gloss of civilian rule vanished in June when Prime Minister Recep Tayyip Erdogan violently suppressed a protest movement in central Istanbul, suggesting that one authoritarianism was being replaced with another. This month’s treason trial brought out sharp divisions between secularists and Islamists, underscoring how Turkey’s nation-building model remains a work in progress.