The influential Muslim cleric lives quietly on a gated 26-acre compound in the Pocono Mountains, where he prays, works, meets admirers and watches from afar as terrorism accusations that have landed him on Turkey’s most-wanted list unfold in court. Rarely seen in public, Fethullah Gulen has long been one of Turkey’s most important scholars, with multitudes of followers in his native country and around the world. More recently, Turkey’s increasingly autocratic president, Recip Erdogan, has accused Gulen of plotting to overthrow the officially secular government from his Pennsylvania idyll some 5,000 miles away. Gulen’s supporters call the charge baseless and,...