Historical clue formulations

• Nonbeliever, now — 2020-01-05
• Party switcher, say — 2012-09-01
• One who loses faith — 2010-05-21
• Deserter — 2009-01-10
• One who's fallen — 2006-09-03
• Forsaker of the faith — 2006-04-16
• Forsaker of the faith — 2000-03-31
• Julian the___ — 1996-05-18