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