Overview
A partisan is a committed member of a political party. In multi-party systems, the term is used for persons who strongly support their party's policies and are reluctant to compromise with political opponents.
United States
The term's meaning has changed dramatically over the last 60 years in the United States. Before the American National Election Study (described in Angus Campbell et al., in The American Voter) began in 1952, an individual's partisan tendencies were typically determined by their voting behaviour. Since then, "partisan" has come to refer to an individual with a psychological identification with one or the other of the major parties. Depending on their political beliefs, candidates may join a party. As they build the framework for career advancement, parties are more often than not the preferred choice for candidates. There are many parties in a system, and candidates often join them instead of standing as an Independent if that is provided for.
In the U.S., politicians have generally been identified with a party. Many local elections in the U.S. (as for mayor) are "nonpartisan." A candidate may have a party affiliation but it is not listed on the ballot. Independents occasionally appear in significant contests but rarely win. At the presidential level, the best independent vote getters were Ross Perot in 1992 and 1996, and John B. Anderson in 1980.
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