The Collaborative International Dictionary of English v.0.48:

mugwump \mug"wump`\, n. [Cf. Algonquin mugquomp a chief.]
   1. A bolter from the Republican party in the national
      election of 1884; an Independent. [Political Cant, U.S.]
      [1913 Webster]

   2. A person who is undecided about an issue, especially a
      political one; a person who takes a neutral stance on an
      issue; a fence-sitter.
      [PJC] Mugwumpery

WordNet (r) 3.0 (2006):

Mugwump
    n 1: someone who bolted from the Republican Party during the
         U.S. presidential election of 1884
    2: a neutral or uncommitted person (especially in politics)
       [syn: mugwump, independent, fencesitter]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "mugwump":
   Fabian policy, Micawberism, Milquetoast, anythingarian, apostate,
   backslider, backwardness, big boy, big chief, big shot, bigwig,
   bolter, collaborationist, collaborator, convert, defector,
   deserter, dilatoriness, fence-sitter, fifth columnist, free lance,
   free spirit, free trader, freethinker, heavyweight, hesitation,
   high-muck-a-muck, hold-off, independent, individualist,
   isolationist, jellyfish, latitudinarian, laxness, leader, liberal,
   libertarian, libertine, lion, nabob, neuter, neutral, nonpartisan,
   nothingarian, procrastination, proselyte, quisling, recidivist,
   recreant, remissness, renegade, renegado, renegate, reversionist,
   rugged individualist, runagate, schismatic, seceder, secessionist,
   separatist, shilly-shally, slackness, slowness, stall,
   strikebreaker, swing vote, temporization, tergiversant,
   tergiversator, third force, third world, traitor, turnabout,
   turncoat, turntail, uncommitted voter, waverer, weakling,
   wobbler



The Devil's Dictionary (1881-1906):

MUGWUMP, n.  In politics one afflicted with self-respect and addicted
to the vice of independence.  A term of contempt.