1) Advocate 2) Advocator 3) An advocate of jansenism 4) Exponent 5) Proponent 
• (n.) A follower of Cornelius Jansen, a Roman Catholic bishop of Ypres, in Flanders, in the 17th century, who taught certain doctrines denying free will and the possibility of resisting divine grace.
Jan'sen·ist noun [ French Janséniste .] (Eccl. Hist.) A follower of Cornelius Jansen , a Roman Catholic bishop of Ypres, in Flanders, in the 17th century, who taught certain doctrines denying free will and the possibility of resisting divine grace. 
[n] - an advocate of Jansenism