Mugwumps were Republicans who supported Democratic candidate Grover Cleveland in the 1884 United States presidential election. They made the party switch because they could not in good faith support the Republican candidate James Blaine of Maine. Many Republicans considered him to be untrustworthy and a fraudulent candidate. This was unusual, in the political stranglehold of Gilded Age politics.

The main issue which angered Republicans and caused them to choke on Blaine's candidacy was the then red-hot issue of political patronage. This consisted of doling out government positions to those who had supported your political party prior to the election. That was before the passage of the Pendleton Act of 1883, which made competency and merit the base qualifications for government positions, rather than political affiliation and appointment by a favorable administration.

In the 1880s, political patronage split the United States Republican Party straight down the middle for several consecutive sessions of U.S. Congress. The party was divided into two warring factions, each with creative names. The side that held the upper hand in numbers and popular support were the Half-Breeds, a faction led by Senator James Blaine of Maine. His political faction were dead-set against any civil service reform. They blocked legislation put forth by their main congressional opponents, the stalwarts, led by Roscoe Conkling of New York. He believed in reform, but only to a certain degree. He realized, probably, that he was unable to achieve a stalwart majority in the U.S. Congress and therefore sought legislation to reduce, at least, the power of his rivals.

Mugwumps were often portrayed as "fence-sitters" with part of their body on the side of the Democrats and the other on the side of the Republicans. The term mugwump may be read a combination of "mug" and "wump", which means respectively the face and the backside (rump). According to Merriam-Webster's Third International Dictionary, however, originally "mugwump" was a Native American word meaning "person of importance."

See also: Mugwump (Miscellaneous Uses), Neo-Mugwump.