5.2 Political Parties

What Parties Do

Political parties are organizations that recruit, nominate, and support candidates for office to win control of government. They simplify choices for voters, mobilize voters, provide a linkage institution between citizens and government, and help organize government by structuring legislative leadership and committee assignments.

Two-Party System & Its Causes

The U.S. has a stable two-party system, reinforced by single-member districts with plurality voting/winner-take-all rules (Duverger's Law) and the Electoral College. Third parties (e.g., ideological, single-issue, splinter parties) rarely win but can act as spoilers, shift debate, or push major parties to adopt their issues.

Party Organization & Change Over Time

Parties operate at national, state, and local levels, running conventions and platforms. Over time, the rise of primaries, campaign finance reform, and media/technology has decentralized party control over nominations, while party polarization has increased ideological distance between Democrats and Republicans, especially in Congress.

Key terms

Political party

An organization that recruits, nominates, and supports candidates for office to gain control of government.

Linkage institution

A structure (like parties, media, or interest groups) connecting citizens' preferences to government policymakers.

Duverger's Law

The theory that single-member district, winner-take-all elections tend to produce a two-party system.

Spoiler party

A minor/third party that draws enough votes from a major candidate to affect the election's outcome.

Party polarization

Growing ideological distance and reduced overlap between the two major parties, increasing partisan conflict.

Try an AP-style question

Which is a main function of political parties?

1. Printing money
2. Enforcing laws
3. Mobilizing voters
4. Writing court opinions