Gerrymandering affects democracy by letting whoever draws the map decide election outcomes before voters get a say. Safe districts replace competitive ones, legislative majorities stop tracking what voters actually chose, incumbents answer to a narrow slice of their party rather than the general public, and federal courts have largely stepped back from policing the practice. In the 2024 U.S. House elections, roughly 70 percent of races were decided by margins exceeding 15 percentage points, and the average winning margin across all 435 seats was 27.3 points. Those numbers are not accidents of geography. They are partly the product of deliberate line-drawing.
How the Manipulation Works
Every ten years, states redraw congressional and legislative districts using new census data. In most states, the legislature controls that process, and that is where the manipulation happens.
Two tactics do most of the work. “Cracking” splits voters who tend to support the same party across several districts so they cannot form a majority anywhere. A neighborhood that would naturally elect its preferred candidate gets carved up and absorbed into surrounding districts where its residents are permanently outnumbered. “Packing” does the opposite. It crams opposing voters into as few districts as possible. The packed party wins those seats by absurd margins, but every vote beyond a bare majority is effectively thrown away.
Both tactics create what analysts call wasted votes: any ballot cast for a losing candidate, plus any vote for a winning candidate beyond the number needed to win. Gerrymandering works by forcing one party to waste far more votes than the other. Researchers quantify the imbalance using the “efficiency gap,” which divides the difference between each party’s total wasted votes by the total votes cast. A large gap suggests the map was drawn to give one side a systematic, unearned advantage in converting votes into seats.
What It Does to Electoral Competition
The most immediate effect is the death of competitive general elections. When mapmakers design districts where one party holds an overwhelming registration advantage, the November race becomes a formality. Any real contest shifts to the primary, and candidates who win safe seats do not need to persuade anyone outside their own party’s base.
That dynamic also discourages strong challengers from entering in the first place. Running for office is expensive, time-consuming, and professionally risky. Few qualified people will make that sacrifice in a district where the outcome is foreordained. Weak challengers make elections even less competitive, which reduces public attention, which makes the seats even safer.
Gerrymandering is not always one party against the other. Sometimes the two parties cooperate. When neither side has enough control to push through a fully partisan map, legislative leaders occasionally strike bipartisan deals that protect all sitting incumbents. Each party keeps its safe seats, and voters lose any realistic chance of holding their representatives accountable at the ballot box.
What It Does to Representation
The Constitution requires congressional districts to contain nearly equal populations so that each person’s vote carries roughly the same weight. The Supreme Court established the principle in Wesberry v. Sanders, holding that “as nearly as is practicable, one man’s vote in a congressional election is to be worth as much as another’s.”1Justia. Wesberry v. Sanders, 376 U.S. 1 (1964) Reynolds v. Sims extended the same logic to state legislatures under the Equal Protection Clause.
Gerrymandering respects the population numbers while gutting the principle behind them. Two districts can have identical populations yet wildly different political compositions. Through cracking and packing, a party that wins only 45 percent of the statewide vote can end up holding a comfortable majority of legislative seats. The legislature then does not reflect what voters chose. It reflects what the mapmakers decided in advance.
Racial minorities are especially exposed. Mapmakers can crack communities of color across multiple districts to prevent them from electing preferred candidates, or pack them into a handful of districts to minimize their influence everywhere else. This form of racial vote dilution has a long, well-documented history in American politics and remains one of the most contested issues in redistricting litigation.
What It Does to Polarization and Policy
Safe seats change who runs and how they govern. When the general election is a foregone conclusion, the primary is the only election that matters. Primary electorates tend to be smaller and more ideologically committed than general election voters. A candidate who takes a moderate stance risks being outflanked by a challenger running to the ideological extreme, and incumbents know it.
The incentive is clear: appeal to the base, avoid compromise, and treat cooperation with the other party as a political liability. Candidates who frame their campaigns as tests of ideological purity win primaries. Those who emphasize pragmatism and deal-making lose them. Over time, that filters out moderates and fills legislatures with members who have no political reason to work across the aisle. Some analysts question whether primaries alone drive polarization to the degree commonly assumed, and reforms like nonpartisan primaries may soften the dynamic. But the combination of safe seats and low-turnout primaries creates real pressure toward the extremes.
The downstream effect is gridlock. Bills with broad public support can stall for years because the legislators who would negotiate them face no electoral penalty for refusing to act. The penalty runs the other direction: cooperate and risk a primary challenger accusing you of betrayal.
Accountability erodes in quieter ways too. Representatives in safe districts can afford to skip town halls, thin out constituent services, and chase national media or party fundraising instead of local concerns. Voters have no realistic way to replace an unresponsive representative. The threat of being voted out is the most basic check on an elected official’s behavior, and gerrymandering neutralizes it for a large share of the legislature.
What the Law Does and Does Not Reach
Federal courts have drawn a sharp line. Racial gerrymandering, where race is the predominant factor in drawing district lines, remains subject to federal court review. Partisan gerrymandering does not.
Partisan Claims Are Closed in Federal Court
The Supreme Court closed the door on federal partisan gerrymandering claims in Rucho v. Common Cause (2019). The Court held that “partisan gerrymandering claims present political questions beyond the reach of the federal courts,” reasoning that federal judges “have no license to reallocate political power between the two major political parties, with no plausible grant of authority in the Constitution, and no legal standards to limit and direct their decisions.”2Supreme Court of the United States. Rucho v. Common Cause, No. 18-422 The ruling effectively ended decades of lower-court efforts to develop a workable test for when partisan map-drawing crosses a constitutional line.3Legal Information Institute (LII). Fourteenth Amendment – Partisan Gerrymandering
The practical impact is large. No matter how extreme a partisan gerrymander, you cannot challenge it in federal court on partisan grounds alone. A state legislature could draw a map that gives one party 70 percent of seats despite winning only 50 percent of votes, and the federal judiciary would have no authority to intervene.
Racial Claims Are Still Live
Racial gerrymandering claims remain fully justiciable. The Fourteenth and Fifteenth Amendments prohibit using race as the predominant factor in drawing district lines, and Section 2 of the Voting Rights Act of 1965 bars redistricting plans that dilute the voting power of racial minorities. In Allen v. Milligan (2023), the Supreme Court affirmed that when a sufficiently large and geographically compact minority group is politically cohesive, and when white bloc voting would otherwise defeat the minority’s preferred candidates, a plan that fails to create a reasonably configured majority-minority district can violate Section 2.4Supreme Court of the United States. Allen v. Milligan, No. 21-1086
The line between racial and partisan gerrymandering sounds clean and gets messy in practice. Because race and party affiliation are often correlated, a map that looks like a racial gerrymander might be defended as merely partisan, and vice versa. Courts regularly have to untangle which factor “predominated.”
State Courts and Structural Reforms
With federal courts off-limits for partisan claims, state courts have become the primary battleground. Several have struck down partisan gerrymanders under their own state constitutions, relying on provisions like “free elections” clauses that have no direct federal equivalent. The reasoning and reach vary by state, and not every state constitution offers the same tools.
Structural reform has centered on independent redistricting commissions. About fifteen states now use some form of commission with primary responsibility for drawing state legislative maps, and several also handle congressional districts. These commissions typically bar sitting legislators, lobbyists, and other political insiders from serving. The degree of independence matters: a commission stacked with partisan appointees and subject to legislative override may not produce meaningfully different maps than the legislature would have drawn itself.
Reform has also targeted the criteria mapmakers must follow. Traditional principles include compactness, contiguity, and preservation of counties and cities. A growing number of states have added rules aimed squarely at gerrymandering: explicit bans on drawing districts to favor or disfavor a party, prohibitions on using partisan data like past election results during map-drawing, and requirements that districts encourage competitiveness. None of these reforms eliminate gerrymandering entirely. Sophisticated mapmakers can satisfy compactness and contiguity while still engineering partisan outcomes. And any reform requiring legislative approval faces an obvious obstacle: the people who benefit most from gerrymandering are the people who would have to vote to end it. The most successful reforms have generally come through ballot initiatives, where voters bypass the legislature.