From Academic Kids
Electoral fusion is an arrangement where two or more political parties support a common candidate, pooling the votes for all those parties. By holding out on major party candidates, minor parties can influence the candidate's platform.
Fusion in the United States
Electoral fusion was once widespread in the United States. "Most of the electoral victories normally attributed to the Grangers, Independents, or Greenbackers in the 1870s and 1880s were a result of fusion between those third party groups and the Democrats." In the late 1800s, however, as minor political parties like the populist People's Party became increasingly successful in using fusion to impact elections, Republican-dominated state legislatures enacted bans against it. One Republican Minnesota state legislator was clear about what his party was trying to do, "We don't propose to allow the Democrats to make allies of the Populists, Prohibitionists, or any other party, and get up combination tickets against us. We can whip them single-handed, but don't intend to fight all creation." (Spoiling for a Fight, 227-228)
Fusion has the highest profile in New York; small parties significant in large part for their fused ballot lines include the Working Families Party, Liberal Party, Conservative Party, and Independence Party.
One of the few current American parties advocating electoral fusion is the New Party, which suffered a defeat when the U.S. Supreme Court refused to recognize fusion as a constitutional right. Fusion has sometimes been used by other recent third parties: for example, the Libertarian Party used fusion to elect four members of the New Hampshire state legislature during the early 1990s.
Occasionally, popular candidates for local office have succeeded in being nominated by both Republican and Democratic Parties. In 1946, Republican California Governor Earl Warren (a future Chief Justice of the United States) managed to win the nominations of the Republican, Democratic, and Progressive Parties.