Caucuses are party-run meetings that can shape who appears on the ballot for Congress and who has the strongest organisational backing. Understanding caucuses helps explain party power, activist influence, and differences across states.

What caucuses are (and why parties use them)

Unlike state-administered elections, caucuses are typically party-controlled, with rules set by party organisations (often within state law constraints).

Caucus participation usually begins with check-in and party-managed procedures (e.g., verifying eligibility and distributing materials). This photo captures the administrative, party-run nature of caucuses, highlighting how they operate more like organized meetings than walk-in polling-place elections. Source

Parties use caucuses to coordinate around a preferred candidate, test organisation, and narrow choices before voters see the final field.

Core purposes in congressional candidate selection

• Selecting a nominee when party rules or state rules allow nomination by caucus or convention rather than a primary.

• Endorsing a candidate to signal “the party’s choice,” influencing donors, activists, and voters.

• Recruiting and screening contenders (encouraging strong candidates to run and weaker candidates to exit).

• Building unity by negotiating among factions to avoid splintered support.

Where caucuses matter most in congressional elections

Nomination without a primary (or instead of one)

In some states or in certain circumstances, parties may rely on a caucus/convention system to choose the party’s nominee for the U.S. House or U.S. Senate. This can occur when:

• The party opts for a convention-style nomination permitted under state/party rules.

• A special election timeline is compressed, and parties use meetings to pick a nominee quickly.

This approach can strengthen party organisations because success depends on relationships with local party leaders, precinct captains, and committed participants.

Influencing the field even when a primary exists

Even when a primary will decide the nominee, caucuses can still influence the field by shaping which candidates are viable:

• Pre-primary endorsements: A caucus endorsement can function like a party “seal of approval.”

• Access to party resources: Endorsed candidates may receive help with volunteers, voter files, and introductions to key donors.

• Signalling to interest groups: Organised groups often treat caucus outcomes as evidence of momentum and invest accordingly.

• Strategic pressure: Party activists may urge multiple candidates to consolidate behind one contender to avoid costly intraparty fights.

How a caucus shapes candidate selection (typical sequence)

Meeting-to-choice mechanics

While formats vary, caucus-based selection often follows a pattern:

• Party members gather at a set location/time (sometimes organised by precinct, county, or district).

• Participants hear speeches, debate, or question candidates.

• Rules determine who can participate (often requiring party registration or proof of affiliation).

• A vote is taken to:

  • Select the nominee directly, or

  • Choose delegates who later select the nominee at a higher-level meeting, or

  • Issue an endorsement that influences subsequent contests.

What this rewards in candidates

Caucuses tend to favour candidates who can:

• Mobilise high-intensity supporters to attend a meeting at a specific time.

• Build relationships with party insiders and activist networks.

• Communicate effectively in small-group settings and sustain grassroots organisation.

Democratic implications and trade-offs

Potential advantages

• Stronger party accountability: Candidates chosen through party meetings may be more closely tied to party platforms and networks.

• More deliberation: In-person discussion can prioritise issue depth over name recognition.

• Faster decision-making: Useful when parties must pick a nominee quickly.

Potential drawbacks

• Lower participation: Caucuses often involve fewer participants than broad-based elections, increasing the influence of activists.

This bar chart compares voter turnout levels across states using primaries versus caucuses in 2016, visually emphasizing the participation gap between the two nomination methods. It reinforces why caucuses can magnify activist influence: when fewer people participate, organized groups can have disproportionate impact. Source

• Representation concerns: Those with flexible schedules, transportation, or stronger political engagement may be overrepresented.

• Perceptions of insider control: Because parties set many rules, caucuses can be criticised as less open than mass voting methods.

These effects help explain why caucuses can meaningfully select candidates in some contexts and influence the field even when voters ultimately decide in an election.