A ward heeler (occasionally "ward-heeler" or just "heeler") is a low-level political operative who solicits votes and performs chores for his political boss or political machine, or sometimes an actual politician who belongs to a small clique that controls a political party for private rather than public ends. It's a slang term first seen in print in 1890, from the days of U.S. politics when someone could cover a ward, a subdivision of a city, on foot, canvassing for votes, putting up signs, and anything else that might benefit the campaign (hence "heel") but there's the idea of a hanger-on following at the heels of his boss; in the 1870s a "heeler" was someone on the lookout for shady work. Because of its connections with political machines, the term has had negative connotations and a ward heeler was often considered to be an unscrupulous character. Booth Tarkington describes one with the words, "He was a pock-pitted, damp looking soiled little fungus of a man who had . . . through the operation of a befitting ingenuity, forced a recognition of his leadership."
The term is now more often used for anyone working on a political campaign and has fewer pejorative overtones than it once did. It can also be used metaphorically, as in "Heaven Help Alabama," an article about Alabama State Supreme Court Justice Roy Moore which says, "Moore had no sooner got himself elected to head the state Supreme Court as God's own ward heeler than he commissioned a two-and-a-half ton monument of the Ten Commandments for the rotunda of the Alabama Judicial Building."