mugwump
A (male) leader; an important (male) person.
A member of the Republican Party who declined to support the party's nominee James G. Blaine (1830–1893) during the 1884 United States presidential election, believing him to be corrupt, and instead supported the Democratic Party's candidate Grover Cleveland (1837–1908).
historical
A person who purports to stay aloof from party politics.
The story of the capture of Vicksburg is the old, old story of failure turned into success, by which man is made immortal. It involves the history of a general who never retraced his steps, who cared neither for mugwump murmurs nor political cabals, who took both blame and praise with equanimity.
One who switches from supporting one political party to another, especially for personal benefit.
Where it comes from
The noun is borrowed from Massachusett mugquomp, mummugquomp (“war leader”). Folk etymology reinterpreted it as referring to a person who sat on the fence with their mug (“face”) on one side and wump (“rump”) on the other, which influenced political cartoons during the 1884 United States presidential election. The verb is derived from the noun.
Adapted from the Wiktionary entry mugwump (CC BY-SA 4.0).