(The following article is taken from the U.S. Department of State publication, USA Elections in Brief.)

When the Founders of the American Republic drafted and ratified the U.S. Constitution in 1787, they did not envision a role for political parties. Indeed, they sought through various constitutional arrangements — such as separation of powers among the executive, legislative, and judicial branches; by federalism; and by indirect election of the president by an Electoral College — to insulate the new republic from parties and factions.

In spite of the Founders' intentions, the United States in 1800 became the first nation to develop nascent political parties organized on a national basis to accomplish the transfer of executive power from one faction to another via an election. The development and expansion of political parties that followed was closely linked to the broadening of voting rights. In the early days of the Republic, only male property owners could vote, but that restriction began to erode in the early 19th century as the result of immigration, the growth of cities, and other democratizing forces, such as the westward expansion of the country. Over the decades, the right to vote was extended to ever larger numbers of the adult population as restrictions based on property ownership, race, and sex were eliminated. As the electorate expanded, the political parties evolved to mobilize the growing mass of voters as the means of political control. Political parties became institutionalized to accomplish this essential task. Thus, parties in America emerged as a part of democratic expansion, and, beginning in the 1830s, they became firmly established, and powerful.

Today, the Republican and Democratic parties — both of them heirs to predecessor parties from the 18th and 19th centuries — dominate the political process. With rare exceptions, the two major parties control the presidency, the Congress, the governorships, and the state legislatures. For instance, every president since 1852 has been either a Republican or a Democrat, and in the post-World War II era, the two major parties' share of the popular vote for president has averaged close to 95 percent. Rarely do any of the 50 states elect a governor who is not a Democrat or a Republican. The number of independent or third-party members of Congress or of state legislatures is extremely low.

In recent decades, increasing numbers of individual voters classify themselves as "independent," and they are permitted to register to vote as such in many states. Yet, according to opinion polls, even those who say that they are independents normally have partisan leanings toward one party or another.

An exception to this general rule can be found at the local level, particularly in small cities and towns, where candidates may not be required to declare any party affiliation, or may run as part of a slate of like-minded office-seekers under the banner of a particular local initiative — such as downtown redevelopment or school construction.

Although the two major parties organize and dominate the government at the national, state, and local levels, they tend to be less ideologically cohesive and programmatic than parties in many democracies. The ability of the major parties to adapt to the nation's political development has resulted in a pragmatic domination of the political process.

Why a Two-Party System?

As noted, Republicans and Democrats have dominated electoral politics since the 1860s. This unrivaled record of the same two parties continuously monopolizing a nation's electoral politics reflects structural aspects of the American political system as well as special features of the parties.

The standard arrangement for electing national and state legislators in the United States is the "single-member" district system, wherein the candidate who receives a plurality of the vote (that is, the greatest number of votes in any given voting district) wins the election. Although a few states require a majority of votes for election, most office holders can be elected with a simple plurality.

Unlike proportional systems popular in many democracies, the single-member district arrangement permits only one party to win in any given district. The single-member system thus creates incentives to form broadly based national parties with sufficient management skills, financial resources, and popular appeal to win legislative district pluralities all over the country. Under this system, minor and third-party candidates are disadvantaged. Parties with minimal financial resources and popular backing tend not to win any representation at all. Thus, it is hard for new parties to achieve a viable degree of proportional representation, and achieve national clout, due to the "winner-take-all" structure of the U.S. electoral system. Why two instead of, say, three well-financed national parties? In part, because two parties are seen to offer the voters sufficient choice, in part because Americans historically have disliked political extremes, and in part because both parties are open to new ideas.

The Electoral College

There is a further impetus toward the two-party solution, and that is the Electoral College system for choosing presidents. Under the Electoral College system, Americans, technically, do not vote directly for the president and vice president. Instead, they vote within each state for a group of "electors" who are pledged to one or another presidential candidate. The number of electors corresponds to the number in a state's congressional delegation, i.e., the number of representatives and senators from that state. Election to the presidency requires an absolute majority of the 50 states' 538 electoral votes.

The absolute majority requirement makes it extremely difficult for a third-party candidate to win the presidency because the individual states' electoral votes are allocated under a winner-take-all arrangement (with two exceptions). That is, whichever candidate receives a plurality of the popular vote in a state — even if it is just a narrow plurality — wins all of that state's electoral votes. In Maine and Nebraska, the statewide popular vote winner is awarded two electoral votes and the winner in each congressional district is awarded one electoral vote. Like the single-member district system, the Electoral College works to the disadvantage of third parties, which have little chance of winning any state's electoral votes, let alone carrying enough states to elect a president.

The founders of the nation devised the Electoral College system as part of their plan to share power between the states and the national government. Under the Electoral College system, the nationwide popular vote for president has no final significance. As a result, it is possible that the electoral votes awarded on the basis of state elections could produce a different result than the nationwide popular vote. In fact, there have been 17 presidential elections in which the winner did not receive a majority of the popular vote cast. The first of these was John Quincy Adams in the election of 1824, and the most recent was George W. Bush in 2000. Some people consider the Electoral College system to be an outmoded relic, while other observers prefer it because it requires presidential candidates to contest the election in many states, rather than just in the most populous ones.

Nebraska's Electoral College meets in December 2004 to cast the state's five electoral votes for president. (© Nati Harnik/AP Images)

Other Barriers to Third Parties

Given the tendency of the system to produce two national parties over the course of time, and with the Democrats and Republicans currently in control of the governmental machinery, it is not surprising that they have created other electoral rules that work to their advantage. For instance, qualifying a new party for the ballot in a state can be an arduous and expensive undertaking, often requiring petitions with tens of thousands of signatures and the ability to attract a sufficient "threshold" proportion of the vote in subsequent elections to remain on the ballot.

America's distinctive nominating process is an additional structural barrier to third parties. Among the world's democracies, the United States is unique in its overwhelming reliance on primary elections to nominate partisan candidates for presidential, congressional, and state offices. As noted, under this type of nominating system, rank-and-file voters in a primary election select their party's nominee for the general election. In most nations, partisan nominations are controlled by the party organizations and their leaders. But in the United States, it is now usually the voters who make the ultimate determination of who the Republican and Democratic nominees will be.

Although this system leads to weaker internal party organizations than is the case in most democracies, this participatory nominating process has contributed to the Republican-Democratic domination of electoral politics. By winning party nominations through primary elections, insurgents or reform candidates can work within the parties to gain access to the general election ballot and thereby enhance their chances of general election victories without having to organize third parties. Thus, the primary nomination process tends to channel dissent into the two major parties and makes it, generally, unnecessary for dissidents to engage in the difficult business of forming a third party. Furthermore, the parties and their candidates tend to adapt electoral strategies to co-opt the message of third party and independent candidates who demonstrate wide appeal.

Broad-Based Support

The Republican and Democratic parties both seek broad-based support, and tend to draw voters from across economic classes and demographic groups. With the exception of African-American and Jewish voters — the vast majority of whom usually vote for the Democratic presidential candidate — both parties draw significant levels of support from virtually every major socioeconomic group in society. The parties also exhibit flexibility with respect to policy positions and do not generally enforce a strict adherence to an ideology or a set of policy goals. Rather, they have traditionally been concerned first and foremost with winning elections and controlling the elective branches of government.

Given their broad socioeconomic bases of electoral support and the need to operate within a society that is largely middle-of-the-road ideologically, American parties have adopted essentially centrist policy positions. As noted, they also demonstrate a high level of policy flexibility. This non-doctrinaire approach enables the Republicans and the Democrats to tolerate great diversity within their ranks, and has contributed to their ability to absorb third parties and protest movements when they have occurred. In general, Republicans are seen as the conservative party — with more of an emphasis on property rights and private accumulation of wealth, and the Democrats are seen as somewhat more to the left, favoring liberal social and economic policies. In practice, when they achieve power, both parties tend to be pragmatic.

Decentralized Party Structures

In addition to being ideologically flexible, the two main American parties are characterized by a decentralized structure. Once in office, a president cannot assume that his party's members in Congress will be loyal supporters of his favored initiatives, nor can party leaders in Congress expect straight party-line voting from members of their party. The Democratic and Republican congressional caucuses (composed of incumbent legislators) are autonomous, and may pursue policies that are in opposition to the president, even if the president is from the same party. Party fundraising for elections is similarly separated, as the Republican and Democratic congressional and senatorial campaign committees operate independently from the national party committees that tend to be oriented to the presidential election. In addition, except for asserting authority over procedures for selecting delegates to national nominating conventions, national party organizations rarely meddle in state party affairs.

This organizational fragmentation reflects the consequences of the constitutional separation-of-powers system — the division of powers among the legislative, executive, and judicial branches of government, both at the federal and state level. The system of divided power may create only limited incentives for party unity between legislators and their party's chief executive. This is broadly true whether we are talking about members of Congress vis-a-vis a president of their own party, or a similar relationship between state legislators and a governor.

The layered system of federal, state, and local governments in the United States provides further impetus for decentralization of the parties by creating thousands of constituencies for officeholders at the federal, state, and local levels. As previously noted, the use of primary elections to nominate candidates also weakens the party organizations by denying them the ability to control the selection of party nominees. Individual candidates, therefore, are encouraged to build their own personal campaign organizations and electoral followings, first to win the primaries and then the general elections.

Public Wariness

In spite of the long and impressive evidence of organized partisanship within the American political system, one ingrained component of American civic culture has been increasing distrust of political parties. The adoption and growth of the primary system for nominating congressional and state candidates is testimony to a populist, or even an anti-party, sentiment within the public. Modern Americans are skeptical about the leaders of their party organizations exercising great power over their government. Public opinion polls consistently reveal that large proportions of the population believe that the parties sometimes do more to confuse the issues than clarify them – and that it would be better if there were no party labels on the ballots.

Parties thus must contend with the problem of a substantial number of voters attaching diminished importance to party identification. One indicator of this is the incidence of ticket-splitting. For instance, a voter may vote for his own party's nominee for president and for the other party's nominee in his district for Congress. Thus, in an age of divided government, presidents often find themselves attempting to govern without a majority in one or both houses of Congress. Divided party control of the executive and legislative branches of government has become a commonplace feature of both the national government and the governments in the 50 states. Some observers believe that voters even prefer the arrangement, because it tends to stifle major government initiatives that might inconvenience voters.

Third Parties and Independent Candidates

Third parties and independent candidates, despite the obstacles discussed previously, have been a periodic feature of American politics. Often they have brought societal problems that the major parties had failed to confront to the forefront of public discourse — and on to the governmental agenda. But most third parties have tended to flourish for a single election and then die, fade away, or be absorbed into one of the major parties. Since the 1850s, only one new party, the Republican Party, emerged to achieve major party status. In that instance, there was a compelling moral issue — slavery — dividing the nation. It provided the basis for candidate recruitment and voter mobilization.

There is evidence that third parties can have a major impact on election outcomes. For example, Theodore Roosevelt's third-party candidacy in 1912 split the normal Republican vote and enabled Democrat Woodrow Wilson to be elected with less than a majority of the popular vote. In 1992, H. Ross Perot's independent candidacy attracted voters who, in the main, had been voting Republican in the 1980s, and thereby contributed to the defeat of the incumbent Republican president, George H.W. Bush. In the extremely close 2000 contest between Republican George W. Bush and Democrat Al Gore, it is possible that had Green Party candidate Ralph Nader not been on the ballot in Florida, Gore might have won that state's electoral votes and thereby the presidency.

Public opinion surveys since the 1990s have consistently shown a high level of popular support for the concept of a third party. In the run-up to the 2000 election, a Gallup Poll found that 67 percent of Americans favored a strong third party that would field candidates for president, Congress, and state offices against Republican and Democratic nominees. It is just such sentiments, plus lavish campaign spending, that enabled Texas billionaire Ross Perot to gain 19 percent of the popular vote for president in 1992, the highest percentage for a non-major-party candidate since Theodore Roosevelt (Progressive Party) won 27 percent in 1912.