Gerrymandering affects elections by deciding the winners before the campaign begins. When the party that controls a state legislature draws district lines to its own advantage, it can turn a modest lead in statewide votes into a durable majority of seats, wipe out competitive races, and lock in results for a full decade. One study of enacted congressional maps found only 34 highly competitive U.S. House seats out of 435, compared with 50 that would exist under nonpartisan alternatives.1National Library of Medicine. Widespread Partisan Gerrymandering Mostly Cancels Nationally but Reduces Electoral Competition The result is fewer real choices at the ballot box and weaker accountability for the people who win.
The Two Tactics That Do the Work
Gerrymandering runs on two techniques that operate together. Cracking splits the opposing party’s voters across several districts so they never make up a majority in any of them. Packing does the reverse, cramming as many opposition voters as possible into a small number of districts where they win by huge margins and waste votes everywhere else. Combined, the two moves let a party with a slim statewide edge collect a disproportionate share of seats.
Odd, sprawling district shapes are the most visible sign, but shape alone doesn’t prove anything. A perfectly ordinary-looking district can be just as gerrymandered if the map-drawer used precinct-level voter data to pick which blocks to include. Modern software tests thousands of maps in minutes and optimizes for partisan advantage at a level of precision that wasn’t available a generation ago.
Votes Cast Versus Seats Won
The clearest effect on elections is the gap that opens between the popular vote and the seat count. A party can win a majority of seats while receiving fewer total votes statewide, because packing wastes the losing side’s ballots in blowout districts and cracking delivers narrow, reliable wins for the party that drew the map.
Gerrymandering also makes legislatures less responsive to shifts in public opinion. The same research on enacted congressional plans found that partisan maps make the U.S. House about 16% less responsive to national vote swings: each additional percentage point of the popular vote translates to roughly 7.8 seats under gerrymandered maps, compared with 9.2 seats under nonpartisan alternatives.1National Library of Medicine. Widespread Partisan Gerrymandering Mostly Cancels Nationally but Reduces Electoral Competition When voters change their minds, the seat count changes less than it should.
Safe Seats and Where the Real Race Moves
Once a district is drawn to give one party a comfortable double-digit lead, the general election becomes a formality. The competitive race shifts to the primary, decided by a smaller and more ideologically committed slice of voters. Incumbents in these districts rarely face serious general-election challengers, which weakens the link between elected officials and the broader public they nominally serve. If a representative doesn’t need your vote to win, your concerns carry less weight in their office.
That structure also shapes how those officials govern. When the only realistic threat is a primary challenger from further along the party’s flank, elected officials have every reason to play to the base and little reason to compromise. Safe districts feed polarization because a representative in a packed or cracked seat can take hard-line positions without electoral risk.
What It Does to Your Vote
For an individual voter, the practical effect depends on which side of the line the map-drawer put you on. If you’re in a packed district, your preferred party wins overwhelmingly, but the extra votes above the winning margin change nothing. If you’re in a cracked district, you’re outnumbered by design, and your side loses even when it would have won under different lines.
Turnout suffers in both situations. When the outcome is a foregone conclusion, the motivation to vote drops, and voters who repeatedly find themselves in the minority often conclude that participating doesn’t matter. Lower turnout in uncompetitive districts means the officials who win there represent an even narrower share of the population than the district’s partisan tilt alone would suggest.
Gerrymandering can also break up communities. When map-drawers split a city, county, or neighborhood between districts to hit a partisan target, residents who share the same local concerns end up with different representatives. A neighborhood that should speak with one voice on zoning, schools, or infrastructure gets divided, and its collective influence gets diluted along with it.
What the Law Does and Doesn’t Stop
A common assumption is that gerrymandering must already be illegal. The reality is that the law treats racial and partisan gerrymandering very differently.
Racial Gerrymandering Is Illegal
Drawing lines to dilute the voting power of racial or language minorities violates both the Fourteenth Amendment’s Equal Protection Clause and Section 2 of the Voting Rights Act.2Department of Justice. Section 2 of the Voting Rights Act The Supreme Court recognized racial gerrymandering as a standalone claim in 1993, holding that a plan so driven by race that it “rationally cannot be understood as anything other than an effort to separate voters into different districts on the basis of race” can be challenged in court.3Legal Information Institute. Shaw v. Reno If race is the predominant factor in drawing a district, the map must survive strict scrutiny. States may also be required to draw majority-minority districts where necessary to keep minority voters from being submerged into the majority and denied an equal chance to elect their preferred candidates.4Constitution Annotated. Amdt14.S1.8.6.6 Racial Vote Dilution and Racial Gerrymandering
Partisan Gerrymandering Is Not Reachable in Federal Court
In 2019, the Supreme Court held in Rucho v. Common Cause that partisan gerrymandering claims are political questions federal courts have no authority to resolve, finding “no plausible grant of authority in the Constitution, and no legal standards to limit and direct their decisions.”5Constitution Annotated. Nonjusticiability of Partisan Gerrymandering Claims The ruling did not say partisan gerrymandering is acceptable; it said federal judges lack manageable standards to police it.
State courts have become the alternative venue. Since Rucho, several state supreme courts have struck down partisan maps under their own free-election or equal-protection provisions, including courts in Ohio, New York, Wisconsin, and Alaska. That path is unstable, though. North Carolina’s supreme court struck down partisan maps in 2022 and then reversed itself the following year after the court’s membership changed, declaring the issue nonjusticiable under the state constitution as well.
Equal Population Is Required
One constitutional constraint applies everywhere. Congressional districts must contain nearly equal populations under Article I, Section 2. The Supreme Court set the rule in 1964, holding that “as nearly as is practicable, one man’s vote in a congressional election is to be worth as much as another’s.”6Justia Law. Wesberry v. Sanders, 376 U.S. 1 (1964) State legislative districts must be substantially equal in population under the Equal Protection Clause.7Justia Law. Reynolds v. Sims, 377 U.S. 533 (1964) Equal population is a floor, not a ceiling. A map can meet one-person-one-vote perfectly and still be gerrymandered for partisan advantage.
What Could Change It
The most common reform takes redistricting out of legislators’ hands. About eleven states use commissions for congressional maps and sixteen for state legislative maps. Commissions typically bar recent officeholders, lobbyists, campaign staff, and party officials from serving, though the design varies enough that results vary too. A commission stacked with partisan appointees behaves much like a legislature.
At the federal level, the proposed Freedom to Vote Act would create a statutory ban on partisan gerrymandering in congressional maps and set statistical tests to flag biased plans, presuming maps with high partisan bias illegal unless the state could prove no fairer map was possible. The bill has not passed Congress.
Measurement has grown more sophisticated. Courts and researchers now use the efficiency gap, which calculates the difference in wasted votes between parties as a share of total votes, and ensemble analysis, which compares an enacted map against thousands of computer-generated alternatives to see whether it’s a statistical outlier. These tools don’t settle the political debate, but they give courts and voters a clearer way to identify when a map crosses from ordinary partisanship into deliberate manipulation.