The conversion, by President Erdogan of Turkey, of the Church of the Holy Saviour at Istanbul into a mosque is a moment to mark. It’s another reminder that the demesne of Atatürk is tilting again away from the West. Though one could say that the fate of the churches was sealed in 1453, when the Ottomans conquered Constantinople, Mr. Erdogan’s escalating hostility to Israel and Byzantium’s past glories spells trouble on the Bosphorus.