Two-Party System

The contemporary political structure of the United States functions as a two-party system dominated by the Republican Party and the Democratic Party. These two parties attract a large majority of votes in all municipal, state, and federal elections and have done so consistently since the era of the American Civil War (1861–1865). A Republican or Democrat has won the presidency in every quadrennial election since 1852, and one party or the other has held a controlling presence in every session of Congress since 1856.

Supporters of the two-party system cite advantages such as the dominance of moderate policy, as it prevents candidates with extreme views from gaining traction among large numbers of voters. The system also usually leads to voter consensus on current issues earning a political mandate, thus ensuring that the overall will of the people is represented in government. Additionally, some believe that the two-party system simplifies elections and improves the efficiency of governance.

Critics of the two-party system, however, charge that the two parties have concentrated power between themselves, preventing marginalized voices and innovative platforms from gaining influence. The two-party system encourages voting along partisan lines rather than based on individual candidate's platforms, personal beliefs, or values. Further, critics warn that the system provides officials with little incentive for bipartisan cooperation while sometimes rewarding inaction and polarization.

The contemporary two-party system in the United States evolved from multiple earlier political paradigms that were also dominated by two parties, such as the Federalists and Anti-Federalists parties that emerged soon after independence. A defining characteristic of the two-party structure is the need for each party to reach as large a voter base as possible to remain competitive in elections. Historically, Republicans and Democrats have tended to advance partisan but relatively moderate platforms designed for broad appeal. Most US elections also use plurality voting, which declares the candidate capturing the most votes in an election its winner regardless of whether the candidate earned more than fifty percent of the vote. This structure allows third parties to field candidates; however, third-party candidates do not typically garner as much support as candidates from the two main parties in US elections.

The two-party system also drives several other familiar elements of American politics, including the electoral college, party conventions, candidate debates, partisan media, and partisan propaganda. The electoral college is the body that chooses the president of the United States through votes cast by electors, who are assigned to states in numbers equal to each state's representation in Congress. The influence of the electoral college makes it extremely difficult (though technically possible) for a third-party candidate to win the presidency, as most voters cast ballots along partisan lines and most states use winner-take-all systems in assigning their electoral college votes. Moreover, the presidential vote passes to a two-party Congress in the event that the electoral college fails to decide the winner, making a third-party candidate win even more unlikely in such a situation.

Party conventions and the candidate nomination process divide US elections into two stages: a primary stage, during which each party conducts internal nominations, and a general stage, in which the chosen party candidates compete against each other in a head-to-head election. Debates exist during both stages, but in general elections, they essentially function to prompt voters to choose between two competing political platforms and visions for their constituencies. Partisan media and propaganda machines also fuel the system, with major networks and news organizations displaying implicit or explicit alignments with either the Republicans or the Democrats. In the mass media age, these institutions have thus functioned as a critical means of guiding voter support along their respective partisan lines.

Historically, the Republican Party has been aligned with conservative and right-wing values and policies, and the Democratic Party has been associated with liberal and left-wing values and policies. Since the twentieth century, Republicans have also generally favored less government regulation and support for social safety net programs, while Democrats have typically favored stronger social safety net programs and centralized regulation that discourages or impedes economic exploitation.

Key elements of the Republican agenda in the twenty-first century include economic policies designed to trigger robust job growth and small business creation, protect existing US jobs, and employ tax strategies that will increase workers' take-home pay and incentivize companies to manufacture goods in the United States. The 2020 Republican platform also aims to address the economic and systemic consequences of the novel coronavirus disease 2019 (COVID-19) pandemic, reduce US economic reliance on China, and resist calls to defund or abolish law enforcement departments. During Donald Trump's presidency, Republicans have also embraced "America first" economic and foreign policies, restrictions to US immigration, the promotion of American exceptionalism, and the defense of traditional American values.

The 2020 Democratic platform states that it prioritizes a safe, cautious, and healthy recovery from the COVID-19 pandemic. It also seeks to make affordable health care universally available and to move toward a strong but fairer and more equitable economic structure that reduces wealth inequality. Democrats also intend to introduce meaningful measures to address climate change and reform US law enforcement and criminal justice systems to end what they perceive to be a pervasive pattern of racialized outcomes that disproportionately and negatively impact minorities. The party also aims to create a more open and inclusive immigration system that removes barriers to achieving legal immigration status and citizenship.

Notably, both parties must balance internal and sometimes competing factions to maintain overall unity. For example, many observers note that the Democratic Party of 2020 contains multiple distinct factions including the "far-left," or progressive, wing that supports equity-based social and economic reforms and a more moderate, centrist wing oriented toward issues like labor protections and economic policy. The Republican Party includes blocs such as the "Christian right," which seeks to advance socially conservative religious values, and a libertarian wing that supports a smaller government and the maximization of civil liberties.

Upon the founding of the United States, several architects of the government, including the authors of The Federalist Papers, expressed concern that political parties could lead to political violence or a concentration of power in a single party that might work against the public interests. Though political violence has arisen in the United States at different times, the two-party system has helped prevent a single party from establishing a single-party dictatorship.

Proponents of the two-party system contend that the system encourages moderate policy, efficient governing, and laws that reflect consensus and compromise. Political scientists have also credited the two-party system with simplifying voters because it allows voters to become informed about the party's platform instead of focusing on every individual candidate. Citizens can also participate in party politics to help shape the overall platform rather than reaching out to every candidate. The nature of the two-party system encourages parties to adopt a platform that will appeal to a wide variety of voters.

While the two-party system discourages politicians with extreme views, its structure also makes it easy for parties to deemphasize or ignore compelling alternative ideas supported by sizable but minority voting blocs. Along similar lines the two-party system encourages parties to focus primarily or exclusively on satisfying the desires of their voter bases instead of working toward compromise through "across the aisle" cooperation. This can drive parties and voters further and further apart on key issues, reducing political discourse to a polarized state, which can impair democratic institutions, stall political processes, and divide the judiciary, all of which can estrange voters and prompt them toward even more polarized extremes.

Crowded primaries have seen candidates with unpopular views and sometimes extremist beliefs secure nomination and sometimes office. The 2020 election, for example, involved the Republican Party nominating some candidates ascribing to the QAnon conspiracy theory and the Democratic Party nominating candidates with progressive policies that alienated some voters. Repeated government shutdowns, stalled federal nominations, and other forms of gridlock in the 2010s call into question whether the two-party system makes governing more efficient or if it encourages division. Further, politicians campaigning to their base have led to officials adopting positions that do not reflect the consensus and on which they refuse to compromise. For example, while public support for reproductive rights has steadily increased over decades, many politicians continue to secure party nominations on their staunch opposition to abortion.

Political polarization occurs when the gap between the prevailing viewpoints of the members of a two-party system becomes so pronounced that partisan lawmakers become unwilling or unable to cooperate with each other. Such divides also affect voters with partisan sympathies, who often develop fervent emotional ties to their own party and strong, negative emotional reactions to opposing viewpoints. Such a situation occurred in the years leading up to the American Civil War, and many analysts agree that political polarization has increased in the twenty-first century.

Experts note that political polarization has many social effects including self-segregation in ideologically insulated communities, loss of trust in social and governmental institutions, and a sense among individuals that their actions and ideas must conform to those expressed by their communities. Some studies have also shown that such polarization can negatively impact the physical, mental, and economic health of politically invested citizens. It can also affect individual behaviors on many levels, influencing consumer purchases, media consumption, online activity, and romantic relationships as people increasingly seek to support social and economic structures that reflect their own views. Some analysts and experts have expressed fears that devaluing and humanizing members of the opposing party may lead to increases in hate crimes and politically motivated attacks that may in turn further entrench political polarization.