The Constitution does not mention political parties, and many founders warned against them. Yet parties formed almost immediately, and from the 1850s onward the contest has been between Democrats and Republicans. Polls regularly find that many Americans would like a third major party, and a growing share of voters identify as independents, but third-party candidates seldom win.
This guide explains why the two-party system persists, the history of third parties, the barriers they face, and proposals to change the rules.
Ranked-choice voting, used statewide in Maine and Alaska, lets voters rank candidates so a vote for a third party can transfer if that candidate is eliminated, but several states have banned it and voters rejected expansions in 2024. Fusion voting, allowed in New York and Connecticut, lets minor parties nominate major-party candidates. Some reformers propose multimember House districts with proportional representation, which would require only a change in federal law. Supporters say these reforms increase choice and reduce polarization, while critics say they confuse voters, slow results, or weaken accountability.
A spoiler is a candidate who draws enough votes from one major candidate to tip the race to the other. Analysts still debate whether Perot cost George H. W. Bush the 1992 election or Nader cost Al Gore the 2000 election, since many third-party voters might otherwise have stayed home or split their votes. Supporters of third parties argue that voters should not have to choose the lesser of two evils, while critics say minor candidates can produce outcomes most voters oppose.
Strom Thurmond in 1948 and George Wallace in 1968 won Southern electoral votes as segregationist candidates, and Wallace was the last third-party candidate to win electoral votes. Ross Perot won nearly 19 percent of the popular vote in 1992 as an independent, focusing attention on the deficit. Ralph Nader's Green Party campaign in 2000 drew 97,000 votes in Florida, where the election was decided by 537. The Libertarian and Green parties regularly appear on ballots, and a few independents serve in Congress, usually caucusing with a major party.
Each state sets its own ballot access rules, and new parties and independents often must gather large numbers of signatures, while major parties qualify automatically. The Commission on Presidential Debates requires 15 percent support in national polls, a threshold no third-party candidate has met since Perot in 1992. Federal matching funds go only to parties that won at least 5 percent in the previous election. Major parties also challenge third-party petitions in court and argue that minor candidates act as spoilers.
Most American elections choose one winner per district or state by plurality, and most states give all their electoral votes to the statewide winner. Political scientists call the resulting tendency toward two parties Duverger's law: voters avoid wasting votes on candidates unlikely to win, and like-minded factions merge into broad coalitions. Primaries also let insurgents work within a major party rather than outside it. Countries with proportional representation typically have more parties.
The Anti-Masonic Party held the first national nominating convention in 1831. The antislavery Free Soil Party helped lay the groundwork for the Republican Party, which replaced the Whigs and elected Abraham Lincoln in 1860. The Populists of the 1890s pushed ideas such as the income tax and direct election of senators that major parties later adopted. Theodore Roosevelt's Progressive Party finished second in 1912 with 27 percent of the vote, the best showing by a third party.
See how parties choose nominees in how primaries and caucuses work, learn why winner-take-all matters in the Electoral College explained, or follow the money in campaign finance explained.