An Enemy Old and New: The Dönme, Anti-Semitism, and Conspiracy Theories in the Ottoman Empire and Turkish Republic Marc David Baer

 The main focal point in Ottoman and Turkish antisemitism is the figure of the Dönme—the descendants of Jews who converted to Islam along with their messiah Shabbatai Tzevi. The focus on the Dönme arises from the perception of the Salonikan-based Young Turks as a cabal of Dönme, or secret Jews. It was immediately in the wake of the 1908 constitutional revolution—which culminated in the dethronement of Abdülhamid II, and ultimately led to the construction of the secular Turkish republic—that antisemitic conspiracy theories centering on the Dönme were first voiced. These arguments were expanded after 1923 to claim that the man who abolished the caliphate and established the secular state, the Salonikan Atatürk, was a Dönme. 

https://muse.jhu.edu/article/526035