Spoiler effect

The spoiler effect is a term to describe the effect of a third party candidacy on a close election, possibly tipping the balance between two relatively close leading candidates. The effect is common in the first-past-the-post election system, in which the candidate that receives a plurality of votes (and not necessarily a majority of votes) wins the election.

One vivid example of the spoiler effect at work was the 2000 U.S. Presidential election. In that election, George W. Bush and Al Gore had a very close election in many states, with neither candidate winning a majority of the votes. Many Gore supporters contended that the votes that went to Ralph Nader, a popular third-party candidate, would have likely been votes for Gore had Nader not been in the election. They contend that Nader's candidacy "spoiled" the election for Gore, by taking away enough votes from Gore in many states to give Bush enough votes to win the electors in those states.

A novel attempt at an end run[?] around the spoiler effect was attempted by numerous groups during the 2000 U. S. election campaign. These groups encouraged and arranged vote swapping[?] between third party supporters in states in which the polls were close and mainstream party supporters in states where a close result was not expected.

The spoiler effect is one of the components contributing to the effect known as Duverger's law, which states that the first-past-the-post election system creates and preserves a two-party system.