Third party (U.S. politics)

Third party, or minor party, is a term used in the United States' two-party system for political parties other than the Democratic and Republican parties. The Electoral College for presidential elections and the plurality voting system for most other elections have established a two-party system in American politics. Third parties are most often encountered in presidential elections and while third-party candidates rarely win elections, they can have an effect on them through vote splitting and other impacts.

With few exceptions, the U.S. system has two major parties which have won, on average, 98% of all state and federal seats. According to Duverger's law two main political parties emerge in political systems with plurality voting in single-member districts. In this case, votes for minor parties can potentially be regarded as splitting votes away from the most similar major party. Third party vote splitting exceeded a president's margin of victory in three elections: 1844, 2000, and 2016.

There have only been a few rare elections where a minor party was competitive with the major parties, occasionally replacing one of the major parties in the 19th century. No third-party candidate has won the presidency since the Republican Party became the second major party in 1856 and won in 1860. Since then, a third-party candidate won states in five elections: 1892, 1912, 1924, 1948, and 1968. 1992 was the last time a third-party candidate placed second in any state, and 1996 was the last time a third-party candidate got over 5% of the vote nationally.