Third parties often shape U.S. politics less by winning office than by pressuring major parties to adopt their ideas. This process, called co-optation, can reshape policy debate while limiting third-party electoral growth.

Co-optation: what it is and why it matters

Co-optation occurs when a major party strategically takes on parts of a third-party agenda to attract its supporters, reduce vote-splitting, and neutralise a challenger’s appeal.

Co-optation matters because U.S. elections are highly competitive and coalition-based. Even when third parties rarely win, they can still:

• introduce or popularise issues that major parties previously ignored

• force major-party candidates to clarify positions

• shift what seems politically “mainstream” over time

How major parties co-opt third-party agendas

Step-by-step pattern

Co-optation commonly follows a predictable sequence:

• A third party identifies an issue gap (an unmet concern among voters).

• The issue gains attention through campaigns, protests, media coverage, or close elections.

• One or both major parties selectively adopt the issue to capture those voters.

• The third party’s distinctiveness fades, reducing its ability to mobilise donations, media attention, and votes.

Tools major parties use

Major parties typically co-opt through:

This 1880 Puck magazine cartoon depicts the Republican and Democratic candidates hammering an “Anti-Chinese” position into their respective party “planks,” dramatizing how major parties can converge on an issue. In co-optation terms, it shows how adopting a position associated with an outside pressure can reduce the distinct political space available to challengers by making the issue “major-party business.” Source

• Party platforms: adding planks that echo third-party demands

• Candidate messaging: using third-party language, slogans, or framing

• Policy proposals: introducing bills, executive plans, or state-level initiatives aligned with the agenda

• Symbolic actions: endorsements, commissions, or high-profile speeches signalling commitment

• Targeted outreach: appealing to a third party’s voter base (e.g., region, ideology, or demographic niche)

Why co-optation reduces third-party success

Voter incentives and strategic voting

When a major party adopts a third party’s key issue, many voters conclude they can pursue the same goal without “wasting” a vote.

This hypothetical figure illustrates Duverger’s law: in plurality elections, minor parties can act as “spoilers,” drawing votes from ideologically similar major parties without winning. Over repeated elections, the diagram shows voters shifting toward the two largest parties to avoid vote-splitting, which helps explain why third parties struggle to remain viable even when they raise salient issues. Source

Co-optation can therefore:

• lower the third party’s perceived viability

• reduce donations and volunteer energy

• weaken ballot access efforts and candidate recruitment indirectly (because enthusiasm drops)

Agenda absorption and lowered distinctiveness

Third parties rely on being seen as uniquely committed to an issue. If a major party credibly claims the same issue, the third party loses:

• issue ownership (being viewed as the most authentic champion)

• media novelty (less coverage when the issue is now “major-party business”)

• bargaining power (fewer votes to threaten major parties with)

A key AP Government takeaway is that co-optation is not purely ideological; it is often strategic. Major parties may adopt only the most popular or least disruptive parts of a third-party agenda, aiming to keep new supporters while avoiding broader internal conflict.

Limits and risks of co-optation

Co-optation can backfire or remain incomplete. Major parties may face:

• internal factional conflict when new positions divide existing coalitions

• credibility problems if voters see adoption as opportunistic rather than genuine

• policy follow-through gaps when campaign promises are not implemented, leaving space for the third party (or a new movement) to re-emerge

• selective adoption that satisfies some voters but alienates others, reshaping turnout or party loyalty

Co-optation is therefore best understood as a recurring feature of competition between broad “big tent” parties and narrower issue-driven challengers, consistent with the syllabus emphasis that incorporating third-party agendas can reduce third-party success by pulling their supporters back into major-party coalitions.