Green Party of the United States in the context of "Voter registration in the United States"

American electoral politics have been dominated by successive pairs of major political parties since shortly after the founding of the republic of the United States. Since the 1850s, the two largest political parties have been the Democratic Party and the Republican Party—which together have won every United States presidential election since 1852 and controlled the United States Congress since at least 1856. Despite keeping the same names, the two parties have evolved in terms of ideologies, positions, and support bases over their long lifespans, in response to social, cultural, and economic developments—the Democratic Party being the left-of-center party since the time of the New Deal, and the Republican Party now being the right-of-center party.

Political parties are not mentioned in the U.S. Constitution, which predates the party system. The two-party system is based on laws, party rules, and custom. Several third parties also operate in the U.S. and occasionally have a member elected to local office; some of the larger ones include the Constitution, Green, Alliance, and Libertarian parties, with the Libertarian being the largest third party since the 1980s. A small number of members of the U.S. Congress, a larger number of political candidates, and a good many voters (35–45%) have no party affiliation. However, most self-described independents consistently support one of the two major parties when it comes time to vote, and members of Congress with no political party affiliation caucus to pursue common legislative objectives with either the Democrats or Republicans.

The American Left refers to the groups or ideas on the left of the political spectrum in the United States. It is occasionally used as a shorthand for groups aligned with the Democratic Party. At other times, it refers to groups that have sought egalitarian changes in the economic, political, and cultural institutions of the United States. Various subgroups with a national scope are active. Liberals and progressives believe that equality can be accommodated into existing capitalist structures, but they differ in their criticism of capitalism and on the extent of reform and the welfare state. Anarchists, communists, and socialists with international imperatives are also present within this macro-movement. Many communes and egalitarian communities have existed in the United States as a sub-category of the broader intentional community movement, some of which were based on utopian socialist ideals. The left has been involved in both the Democratic and Republican parties at different times, having originated in the Democratic-Republican Party as opposed to the Federalist Party.

Although left-wing politics came to the United States in the 19th century, there are currently no major left-wing political parties in the country. Despite existing left-wing factions within the Democratic Party, as well as minor third parties such as the Green Party, Communist Party USA, Party for Socialism and Liberation, American Communist Party, Workers World Party, Socialist Party, and American Solidarity Party (a Christian democratic party leaning left on economics), there have been few representatives of left-leaning third parties in Congress. Academic scholars have long studied the reasons why no viable socialist parties have emerged in the United States. Some writers ascribe this to the failures of socialist organization and leadership, some to the incompatibility of socialism with American values, and others to the limitations imposed by the United States Constitution. Vladimir Lenin and Leon Trotsky were particularly concerned because it challenged orthodox Marxist beliefs that the most advanced industrial country would provide a model for the future of less developed nations. If socialism represented the future, then it should be strongest in the United States. While branches of the Working Men's Party were founded in the 1820s and 1830s in the United States, they advocated land reform, universal education and improved working conditions in the form of labor rights, not collective ownership, disappearing after their goals were taken up by Jacksonian democracy. Samuel Gompers, the leader of the American Federation of Labor, thought that workers must rely on themselves because any rights provided by government could be revoked.

Christopher Hitchens (13 April 1949 – 15 December 2011) was a British and American author, polemicist, debater and journalist who in his youth took part in demonstrations against the Vietnam War, joined organisations such as the International Socialists while at university and began to identify as a socialist. However, after 9/11 he no longer regarded himself as a socialist and his political thinking became largely dominated by the issue of defending civilization from terrorists and against the totalitarian regimes that protect them. Hitchens nonetheless continued to identify as a Marxist, endorsing the materialist conception of history, but believed that Karl Marx had underestimated the revolutionary nature of capitalism. He sympathized with libertarian ideals of limited state interference, but considered libertarianism not to be a viable system. In the 2000 U.S. presidential election, he supported the Green Party candidate Ralph Nader. After 9/11, Hitchens advocated the invasion of Iraq. In the 2004 election, he very slightly favored the incumbent Republican President George W. Bush or was neutral and in 2008 he favored the Democratic candidate Barack Obama over John McCain despite being critical of both of them.