Why Two Political Parties?

What are political parties?

Political parties are voluntary associations of voters, candidates, and activists who share ideological and policy goals. The goal of a political party is to elect their candidates to office and enact policies that reflect the views of their supporters.

Most Americans identify as members of one of the two major political parties: the Democrats and the Republicans. In recent presidential and congressional elections, over 90% of Americans voted for candidates from the party with which they identify.

Depending on how the question is asked, up to a third of Americans report being independents with no party affiliation. However, research has shown that most independents are so-called stealth partisans—people who consistently vote for one Party’s candidates, but view being independent as a more thoughtful and knowledgeable choice.  

Why does the U.S. have only two major political parties?

Over the last generation, virtually all candidates elected to the presidency, Congress, state legislatures, and governorships have run as either Democratic or Republican nominees. Nationwide, there are over 400 other political parties, including the Libertarians, Democratic Socialists, Greens, and Constitutional parties. These organizations compete in only a few contests and rarely are successful in getting candidates they support elected into office.

Throughout American history, many voters have held negative views of the major parties. According to a 2023 Pew Research Center Poll, 37% of Americans support the idea of introducing a new third party. In July 2025, Elon Musk announced he was creating a new party called The American Party. What are the chances that this Party can successfully elect candidates to office?

The political science-based answer is a result known as Duverger’s Law: countries that elect candidates with single-member districts and plurality voting generally have only two major political parties. The United States is one such country. Others include Australia, Canada, and the United Kingdom. In all of these countries, third parties sometimes form and win some elections, but generally disappear from politics within a few years. If the third parties are able to survive, it is usually by replacing one of the major parties.  

Two factors drive Duverger’s Law. The first is the mechanical effect. With single-member districts and plurality voting, losing parties don’t receive any legislative seats, so receiving 10% of the vote is equivalent to receiving 0%. As a result, candidates have strong incentives to compete for major-party nominations, as these nominees are much more likely to win enough votes to get elected. The second factor is the psychological effect: because third-party candidates are unlikely to win, citizens are often reluctant to vote for them.  

Many other countries, especially in Europe, elect legislators using proportional representation (PR), where citizens vote for parties rather than candidates. Under PR, if Party A receives 50% of the total vote, it is allocated 50% of legislative seats. If Party B receives 10% of the vote, it will be entitled to 10% of the legislative seats. In PR systems, small parties often survive because they can form alliances with larger parties in the legislature to control the government and enact their preferred policies.

Would it make a difference in the U.S.A. if there were more political parties?

While there are many political parties in America, most Americans choose to identify with one of the two major parties and vote for that party’s candidates. Of course, most of the time, Americans must choose between a Republican and a Democrat. What if a third party ran well-funded, experienced candidates across the nation? Such a party would need to collect signatures to secure ballot access nationwide, something that the major parties typically earn automatically. How many voters might switch to this new party?  

One recent analysis by political scientist Elliot Morris quantified this number by counting the number of Americans who are (a) registered to vote, (b) not strongly tied to one of the major parties, and (c) not strong supporters of President Trump. His calculations indicated less than 20% of Americans were potential members of a third party.

The number became even smaller when Morris added assumptions about a new party’s platform (for example, a party that supports measures to reduce the budget deficit). Morris concluded that the potential number of party switchers was less than 5% of the population, which is likely insufficient for a new party to be successful

The Takeaway

Duverger’s Law tells us that U.S. is unlikely to have more than two major political parties, unless it changes the way it elects candidates to political offices.

While many Americans say they want a new political party, an analysis of survey data suggests that relatively few would support a new party’s candidates.