Lesson 13 min 20 XP
Gerrymandering & Redistricting
How drawing district lines can predetermine election outcomes, and the ongoing fight over fair maps.
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How drawing district lines can predetermine election outcomes, and the ongoing fight over fair maps.
Gerrymandering is the deliberate manipulation of electoral district boundaries to advantage a political party, group, or incumbent. The term dates to 1812, when Massachusetts Governor Elbridge Gerry approved a district so contorted it resembled a salamander. The practice is as old as single-member districts themselves, but modern computing and detailed voter data have made it far more precise and effective. Where a 19th-century mapmaker worked with county-level guesses, today's operatives can draw lines block by block using precinct returns, party registration, and consumer data, then simulate thousands of maps to find the one that squeezes out the most seats.
There are two main techniques. 'Packing' concentrates the opposing party's voters into a few districts where they win by overwhelming margins, wasting their surplus votes. 'Cracking' spreads the opposing party's voters across many districts so they fall short of a majority in each one. Used together, these techniques can transform a 50-50 state into one where the gerrymandering party wins 70 percent of seats. The key idea is the 'wasted vote': every vote cast for a losing candidate, plus every vote beyond the bare majority a winner needs, is wasted. Gerrymandering is the art of making the other side waste more votes than you do.
Suppose a state has 10 equal districts of 100 voters each (1,000 voters total), split 500 Party A and 500 Party B statewide. A neutral map might give each party about 5 seats. Watch what packing and cracking do instead.
| Districts | Party A voters | Party B voters | Seats won |
|---|---|---|---|
| 2 'packed' B districts | 15 each (30) | 85 each (170) | B: 2 |
| 8 'cracked' districts | ~59 each (470) | ~41 each (330) | A: 8 |
| Total | 500 | 500 | A: 8, B: 2 |
With an even statewide vote, Party A takes 8 of 10 seats. The 'efficiency gap' formalizes this: it is the difference between the two parties' wasted votes, divided by total votes. Party B wasted its votes twice, by burying 170 supporters in blowout losses and by falling just short in eight districts, while Party A won each seat efficiently with narrow margins. Reformers proposed the efficiency gap as a court-usable standard in Whitford v. Gill (Wisconsin), but the US Supreme Court declined to adopt it, remanding the case in 2018 on standing grounds. The metric survives as an analytical tool even though courts never enshrined it.
In the United States, most district boundaries are drawn by state legislatures, which means the party in power after each census controls the process. This creates an enormous incentive to gerrymander. After the 2010 census, Republicans controlled redistricting in states covering 213 congressional districts; Democrats controlled just 44. The resulting maps helped Republicans maintain their US House majority even when Democrats won more total votes nationwide in 2012.
Several states have adopted independent redistricting commissions to depoliticize the process. California established a citizens' commission in 2008, and Arizona, Colorado, Michigan, and Virginia have followed with various models. Some countries, like Australia, Canada, and the UK, use independent boundary commissions by default, treating partisan redistricting as obviously corrupt. The US remains an outlier in allowing legislators to choose their own voters.
In Rucho v. Common Cause (2019), the US Supreme Court ruled 5-4 that partisan gerrymandering claims are 'political questions' beyond the reach of federal courts. Chief Justice Roberts wrote that while excessive partisanship in redistricting is 'incompatible with democratic principles,' the Court could find no manageable standard for judging when it goes too far. This effectively closed federal court challenges to partisan gerrymandering, shifting the fight to state courts and ballot initiatives.
Importantly, racial gerrymandering remains justiciable. Under the Voting Rights Act and the Equal Protection Clause, federal courts still strike down maps that dilute or unduly concentrate voters by race. The line between partisan and racial motive is blurry, since race and party correlate strongly in much of the US, and litigants now often reframe partisan claims in racial terms to keep them in federal court. State constitutions have become the main battleground: the Pennsylvania Supreme Court threw out the state's congressional map in 2018 under its own constitution's free-elections clause.