Political parties make a major contribution to American government by linking citizens and government, overcoming some of the fragmentation of government that separation of powers and federalism can produce, and creating an articulate opposition.

American political parties offer the average voter a choice in terms of ideology, membership, and policy positions (platform). The differences may not always be evident, however, because electoral forces create incentives for parties to take moderate positions, drawing the parties together. At the same time, party activists who are committed to the values and policies of a particular party play a key role in pushing the parties apart and keeping them ideologically distinct, leading to increasing partisan polarization.

The two primary activities of parties are electioneering (getting candidates elected) and governing (all the activities related to enacting party policy agendas in government).

American history reveals at least five distinct party eras. These are periods of political stability when one party has a majority of congressional seats and controls the presidency. A realignment, or new era, occurs when a different party assumes control of government. Party politics today may be undergoing both a realignment and a dealignment, resulting in greater numbers of voters identifying themselves as independents.

America’s two-party system is relatively moderate, decentralized, and increasingly disciplined. Although the rules are designed to make it hard for third parties to break in, numerous third-party movements have arisen at different times to challenge the two dominant parties.

While public disenchantment with political parties may be increasing, parties remain one of the most accessible avenues for citizen participation in government. Although recent elections may lead some observers to believe that third parties have the potential to overtake the two major political parties, history shows and experts agree that such parties tend to represent the extreme point of view of one of the major parties, and they end up losing influence in the long run.