AP® United States Government and Politics · Unit 2 · Topic 2.3
Polarization and Partisan Voting
Polarization means Democrats and Republicans in Congress have moved ideologically apart until almost none of them overlap, so party label now predicts a member's vote almost perfectly. That lets a bare majority govern alone and makes divided government produce gridlock.
Political scientists score every member of Congress on an ideology scale built from their actual roll-call votes, not their speeches. Plot those scores from the 1970s to today and you see the two parties pull apart like a rubber band stretching: in the 1970s there was a wide overlapping middle, with conservative Southern Democrats and liberal Northeastern Republicans voting near each other. That overlap has nearly vanished. The most conservative Democrat today is still well to the left of the most liberal Republican. This is a structural change in how members vote, not just a change in tone.
That sorting changes what a majority can do. When party and ideology line up almost perfectly, members rarely cross party lines, so leadership can count on nearly every member of its party to vote together. A party holding just 218 of 435 House seats, the bare minimum for a majority, can still control the floor agenda, block the other party's bills, and pass its own on a near party-line vote, because winning only requires a simple majority and almost nobody defects. Fifty years ago, crossover votes made outcomes less predictable; now the roll call is often a formality.
This connects directly to what happens when control splits between Congress and the presidency. Divided government means a polarized House or Senate majority passes bills the president opposes, or a president's agenda dies in a chamber controlled by the other party. Landmark legislation becomes rare, and government relies more on unilateral tools like executive orders or agency rulemaking to get anything done at all.
Key terms
- Polarization
- The ideological distance between the two parties in Congress growing wider over time, measured by shrinking overlap in voting records.
- Ideology score
- A number derived from a member's roll-call votes that places them on a liberal-to-conservative scale.
- Party-line voting
- A pattern where nearly all members of one party vote one way and nearly all of the other party vote the opposite way.
- Divided government
- A situation where one party controls the presidency and the other controls one or both chambers of Congress.
- Gridlock
- A slowdown in passing legislation that results when opposing parties hold veto points and cannot agree.
Watch it explained
- How it worksWalk me through House ideology scores spreading apart from the 1970s to today.
- How it worksHow does party-line voting turn a 218-seat majority into total control of the floor?
- Going furtherWhat happens to the number of laws passed when one party holds Congress and the other the presidency?
- Common mistakeWhy isn't polarization just the two parties disagreeing more loudly than before?
Check yourself
End of topic.