mugwump a neutral or uncommitted person (especially in politics)
noncandidate someone who has announced they are not a candidate; especially a politician who has announced that he or she is not a candidate for some political office
party boss,
political boss,
boss a leader in a political party who controls votes and dictates appointments; "party bosses have a reputation for corruption"
party liner,
party man a member of a political party who follows strictly the party line
republican a tributary of the Kansas River that flows from eastern Colorado eastward through Nebraska and Kansas
sachem a chief of a North American tribe or confederation (especially an Algonquian chief)