Trojan horse apostate backslider bolter collaborationist collaborator convert crypto defector deserter fellow traveler fifth column fraternizer mugwump proselyte quisling recidivist recreant renegade renegado renegate reversionist runagate saboteur schismatic seceder secessionist security risk separatist strikebreaker subversive tergiversant tergiversator traitor turnabout turncoat turntail underground