AP® United States Government and Politics review sheet from Aim for Five (aimforfive.com/gov/units/5/5-5)
Unit 5 · Topic 5.5
5.5 Third-Party Politics
Third-party and independent candidates rarely win in the U.S. because most elections are winner-take-all contests in single-member districts, which reward the two largest parties. Proportional representation systems, by contrast, give parties seats according to their share of the vote. Third parties still matter: major parties often adopt their popular ideas, which removes the third party's main appeal.
Key terms
- third party
- winner-take-all
- single-member district
- proportional representation
- two-party system
Why the U.S. has a two-party system
In a single-member district system, each district elects one representative. Combined with a winner-take-all (plurality) rule, the candidate with the most votes wins, even if it isn't a majority, and everyone else gets nothing. A party that finishes second or third everywhere can win zero seats.
Because of this, voters often avoid “wasting” their vote on a candidate unlikely to win, and politicians with similar views unite under one of two big parties. Political scientists call this tendency Duverger's law. The Electoral College reinforces it, since 48 states and D.C. award all their electors to the statewide winner.
Proportional representation
In proportional representation (PR), used in many democracies, parties win legislative seats in proportion to their share of the vote. A party with 15 percent of the vote gets about 15 percent of the seats. PR encourages more parties, gives smaller parties a voice, and often requires coalition governments. Some countries use mixed systems with both districts and proportional seats.
| Feature | Winner-take-all, single-member districts | Proportional representation |
|---|---|---|
| Who wins | The top vote-getter in each district | Parties, roughly in proportion to their vote share |
| Number of major parties | Usually two | Often several |
| Small parties | Rarely win seats | Can win seats with modest support |
| Governing | Often one party controls a chamber | Often coalitions of parties |
Other barriers
- Ballot access: third parties often must gather many signatures to get on each state's ballot.
- Debates: the Commission on Presidential Debates has required candidates to reach 15 percent in national polls, which third-party candidates rarely do.
- Money and media: donors and coverage flow to candidates who can win.
- Spoiler fear: voters worry a third-party vote will help the major-party candidate they like least.
Why third parties still matter
Third parties often push ideas that a major party later adopts, and when that happens the major party absorbs the third party's voters. This is a main reason third parties tend to fade after a strong showing.
| Third party or candidate | Result | Impact |
|---|---|---|
| Populist Party (1892) | Won 22 electoral votes | Its calls for a graduated income tax and direct election of senators later became the 16th and 17th Amendments |
| Progressive (Bull Moose) Party, Theodore Roosevelt (1912) | About 27% of the popular vote, finishing ahead of the incumbent Republican | Split the Republican vote, helping Woodrow Wilson win; many progressive reforms were later adopted |
| Ross Perot, independent (1992) | About 19% of the popular vote, zero electoral votes | Made the federal deficit a major issue that both parties then addressed |
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Seats under two systems
A party wins 20% of the vote in every one of a state's 10 districts but never finishes first. How many seats does it win under single-member, winner-take-all districts? About how many would it win under proportional representation? What does this show?
Show the solutionHide the solution
- Step 1: Winner-take-all: only the top vote-getter in each district wins. The party never finishes first, so it wins 0 of 10 seats.
- Step 2: Proportional representation: seats follow vote share. 20% of 10 seats is 2 seats.
- Step 3: Interpret: the same voter support yields 0 seats in one system and 2 in the other, showing why winner-take-all rules discourage third parties.
Answer: 0 seats under winner-take-all and about 2 under proportional representation, which shows how winner-take-all systems shut out smaller parties.
Common mistakes
- Saying the Constitution creates a two-party system. It doesn't mention parties; the two-party system results from election rules and practices.
- Thinking third parties have no impact because they rarely win. They shape debates, and major parties absorb their ideas.
- Confusing proportional representation with the Electoral College. Most states award electors winner-take-all, not proportionally.
On the exam
- Expect questions asking why third parties struggle. Winner-take-all, single-member districts is the strongest answer.
- Know at least one example of a third party whose ideas were later adopted by a major party.
Connected topics
Videos
Check yourself
4 questions on 5.5 Third-Party Politics. Pick an answer to see if you got it, and why.
| Party | Share of the vote (%) | Seats won with 100 single-member districts | Seats won under proportional representation |
|---|---|---|---|
| Party A | 45 | 61 | 45 |
| Party B | 40 | 39 | 40 |
| Party C | 15 | 0 | 15 |
Hypothetical election for a 100-seat legislature
Which conclusion is best supported by the data?
Which feature of single-member, winner-take-all districts best explains Party C's result?
Party C's main proposal becomes popular, and Party A adds it to its own platform. What is the most likely effect on Party C?
In one state, a new party's candidates must collect signatures from 5% of registered voters to get on the ballot, while the two major parties' nominees are listed automatically. This rule best illustrates
0 of 4 answered