Gerrymandering

Gerrymandering is the practice of drawing election district boundaries to advantage a political party, racial or ethnic group, or incumbent. Since the Supreme Court held in Rucho v. Common Cause (2019) that partisan gerrymandering claims are beyond the reach of federal courts, the fight over district lines has moved to state courts, independent commissions, ballot measures, and, in 2025 and 2026, a wave of mid-decade congressional redistricting in at least six states. A 2023 simulation study found that partisan gerrymandering in the 2020 cycle was widespread but mostly canceled out nationally, while it reduced electoral competition.

In plain words: every ten years, after the census, states redraw the lines that decide which voters are in which district. Whoever draws the lines can often predict who will win. Drawing them to help one side is called gerrymandering. Federal courts have said they will not stop the partisan kind. That leaves the job to states, voters, and commissions. This page explains how it works, how it is measured, what has been tried, and why reasonable people still disagree.

The problem, defined precisely

Gerrymandering depends on a few technical terms that are often blurred in public debate.

Apportionment. Dividing U.S. House seats among the states after each census. Redistricting is drawing the boundaries of districts within a state.⁠⁸

Partisan gerrymander. A map drawn to advantage one political party.

Racial gerrymander. A map in which race predominates in drawing lines. Under the Constitution this triggers strict scrutiny, the most demanding level of judicial review.⁠⁵

Vote dilution. A claim, under Section 2 of the Voting Rights Act, that a map gives minority voters less opportunity to elect representatives of their choice.⁠⁵

Cracking and packing. The two basic techniques. As the Supreme Court described them in Gill v. Whitford: “Cracking means dividing a party’s supporters among multiple districts so that they fall short of a majority in each one.” “Packing means concentrating one party’s backers in a few districts that they win by overwhelming margins”.⁠²

Wasted votes and the efficiency gap. A wasted vote is one cast for a losing candidate, or for a winning candidate beyond what was needed to win. The efficiency gap compares each party’s wasted votes across all districts.⁠²

Ensemble or simulation analysis. A method that generates large numbers of alternative maps under neutral rules and compares the enacted map with that distribution.⁠⁶

Commission. A body other than the legislature that draws or advises on maps. The Congressional Research Service (CRS) distinguishes commissions with primary responsibility, advisory commissions, and backup commissions used if the legislature deadlocks.⁠⁷

Mid-decade redistricting. Redrawing maps between censuses. According to CRS, it “is prohibited by neither the U.S. Constitution nor federal law”.⁠⁸

Scale and evidence

Gerrymandering’s measured scale depends on whether one looks at national House control, individual states, or competition.

National seat effects. Christopher Kenny, Cory McCartan, Tyler Simko, Shiro Kuriwaki, and Kosuke Imai compared the House under enacted 2020-cycle maps with simulated nonpartisan alternatives. They found partisan gerrymandering was widespread, but most of its bias canceled out nationally, leaving Republicans an average of two additional seats; geography and redistricting rules added a moderate pro-Republican bias; and gerrymandering reduced electoral competition and made the House less responsive to shifts in the national vote.⁠⁶

Who draws the maps. After the 2020 census, commissions had primary responsibility for congressional lines in 11 of the 44 states apportioned more than one House seat. Colorado, Michigan, New York, and Virginia adopted such commissions after the 2010 census. Iowa uses nonpartisan legislative staff whose maps the legislature must approve; Maine, Maryland, New Mexico, Rhode Island, and Utah have advisory commissions; and Connecticut, Indiana, and Ohio use backup commissions. In total, 21 states have commissions associated with congressional redistricting in some way. In most states the legislature still draws congressional lines.⁠⁷

The 2025 to 2026 mid-decade wave. CRS reports that “lawmakers in a number of states (including California, Missouri, North Carolina, Ohio, Texas, and Utah)” redrew congressional maps ahead of the 2030 census.⁠⁸ In California, voters approved Proposition 50 on November 4, 2025, by 7,453,339 votes (64.4%) to 4,116,998 (35.6%). Its official ballot title was “Authorizes Temporary Changes to Congressional District Maps in Response to Texas’ Partisan Redistricting”.⁠⁹ California’s congressional districts had been the responsibility of its Citizens Redistricting Commission, created by the Voters FIRST Act in 2008 and assigned congressional districts by the Voters FIRST Act for Congress in 2010.⁠¹⁰

These measures answer different questions. The national figure says little about any single state, and a state where the map is heavily skewed can coexist with a national total close to even.

Causes and competing explanations

Gerrymandering has structural causes, and analysts disagree about which matter most.

Self-interest of line drawers. Historically, state legislatures have set congressional boundaries, and CRS notes concerns “about conflicting incentives, if the process is used by incumbents to help boost their parties’ electoral gains”.⁠⁷

Technology and data. Precise voter data and mapping software make it easier to draw maps that hold up across elections. The Supreme Court’s majority in Louisiana v. Callais pointed to “the increased use and capabilities of computers in drawing districts and creating illustrative maps” as a development that changes how courts should evaluate claims.⁠⁵

Political geography. Not all bias is intentional. Kenny and colleagues attribute part of the pro-Republican tilt to geography and redistricting rules, separate from deliberate gerrymandering.⁠⁶ How to separate the two in a given state is a recurring dispute.

Withdrawal of federal courts. In Rucho v. Common Cause (June 27, 2019), Chief Justice Roberts wrote for a 5 to 4 majority: “We conclude that partisan gerrymandering claims present political questions beyond the reach of the federal courts.” The Court acknowledged that “excessive partisanship in districting leads to results that reasonably seem unjust,” and pointed to states and Congress as remaining avenues.⁠¹ Justice Kagan’s dissent began: “For the first time ever, this Court refuses to remedy a constitutional violation because it thinks the task beyond judicial capabilities”.⁠¹ Earlier, in Gill v. Whitford (2018), the Court had sent a challenge back because plaintiffs “failed to demonstrate Article III standing”.⁠²

The interaction of race and party. On April 29, 2026, in Louisiana v. Callais, the Court held 6 to 3 that because the Voting Rights Act did not require Louisiana to create an additional majority-minority district, the state’s map (SB8) was “an unconstitutional racial gerrymander.” Justice Alito’s majority opinion held that Section 2, properly read, “imposes liability only when the evidence supports a strong inference that the State intentionally drew its districts to afford minority voters less opportunity because of their race,” and that it “does not intrude on States’ prerogative to draw districts based on nonracial factors, including to achieve partisan advantage.” The majority also said Rucho created “an incentive for litigants to exploit §2 for partisan purposes”.⁠⁵ Justice Kagan, joined by Justices Sotomayor and Jackson, dissented from what she called “this latest chapter in the majority’s now-completed demolition of the Voting Rights Act”.⁠⁵ Supporters and critics agree the decision changes how race-based and party-based districting claims interact; they disagree sharply on whether that change protects or harms minority voters.

Retaliation dynamics. When one state redraws for advantage, others may answer. California’s Proposition 50 named Texas’s redistricting in its ballot title.⁠⁹ Whether such responses deter or escalate is an open question.

Who is harmed

Gerrymandering’s harms fall on several groups, and the size of each harm depends on the measure.

Voters in uncompetitive districts have less influence over the general election outcome. Kenny and colleagues found gerrymandering reduced competition.⁠⁶ Where general elections are not competitive, primaries may carry more weight; see Primary elections and Polarization.

The national electorate loses responsiveness: the House changes less when national opinion shifts.⁠⁶

Supporters of the disadvantaged party in a particular state can be underrepresented relative to their vote share even if national effects offset.

Minority voters’ position is contested after Callais. The dissent argues they lose a key protection; the majority argues that Section 2 as read before invited race-based districting the Constitution forbids.⁠⁵

Accountability can suffer under either legislatures or commissions. Legislators drawing their own districts face the incentive problem above. Commissions, CRS notes, “can sometimes be structured in ways that may make them less publicly accountable than elected state legislatures”.⁠⁷

What has been tried elsewhere

Reforms have been tried in federal courts, state courts, commissions, and Congress, with uneven results.

Federal litigation. Attempts to have federal courts set a standard for partisan gerrymandering ended in Rucho.⁠¹ Quantitative tests such as the efficiency gap were presented to the Court in Gill but did not produce a ruling on the merits.⁠²

State courts. In Moore v. Harper (June 27, 2023), the Court held 6 to 3 that “the Elections Clause does not insulate state legislatures from the ordinary exercise of state judicial review,” rejecting the strongest form of the claim that legislatures alone control federal election rules.⁠⁴ State constitutions and courts therefore remain a check, but their standards and willingness to act vary by state.

Independent commissions. In Arizona State Legislature v. Arizona Independent Redistricting Commission (2015), the Court held 5 to 4 that “the Elections Clause permits the people of Arizona to provide for redistricting by independent commission”.⁠³ Colorado, Michigan, New York, and Virginia adopted congressional commissions after the 2010 census.⁠⁷ CRS notes that proponents expect commissions to prevent partisan gerrymandering and create more competitive districts, while others argue “the effect of redistricting methods on electoral competitiveness is overstated” and that commission structures can let political considerations remain; bipartisan designs “may seek to balance political or partisan interests, rather than remove them entirely”.⁠⁷

Commissions overridden. Commissions are not permanent. California voters authorized temporary changes to the commission’s congressional map through Proposition 50 in response to another state’s redistricting.⁠^9,10 That shows a commission in one state does not stop competition between states.

Federal legislation. The House passed bills requiring independent commissions in the 116th and 117th Congresses, and more were introduced in the 119th. CRS describes the current position as one in which “Congress may continue to allow states to establish their own congressional redistricting processes”.⁠⁷

The strongest arguments across the political spectrum

Positions on gerrymandering cut across party lines, partly because each party gerrymanders where it can.

The neutral-process argument. Reformers argue that those who benefit from a map should not draw it, and that commissions, clear criteria, and public input produce maps voters can trust.⁠⁷ The weak point is that commissions can be designed to balance party interests rather than remove them, and can be overridden, as California shows.⁠⁹

The democratic accountability argument. Others argue that districting is an inherently political act that belongs with elected, accountable legislators, and that unelected commissions or judges are less answerable to voters. The Rucho majority pointed to the political branches as the proper avenue.⁠¹ The weak point is the conflict of interest built into legislators drawing their own districts.

The federalism and judicial-restraint argument. Many conservatives and textualists hold that federal courts lack a manageable standard for “too much” partisanship and that the Constitution leaves districting to states and Congress.⁠¹ The Callais majority adds that Section 2 must be read within Congress’s power to enforce the Fifteenth Amendment’s ban on intentional discrimination.⁠⁵ The weak point, pressed by the dissents, is that a right without a remedy may not function as a right.⁠^1,5

The civil rights argument. Advocates for minority voting rights argue that race and party are intertwined in many states, that Section 2 was the main tool against dilution, and that Callais leaves minority communities exposed.⁠⁵ The weak point, in the majority’s view, is that remedying dilution by drawing districts on the basis of race can itself violate equal protection.

The unilateral disarmament argument. Some argue that a state should not give up partisan mapping while rival states keep it, and that only a national rule should end the practice. California’s Proposition 50 reflects this logic.⁠⁹ Critics reply that answering one gerrymander with another normalizes the practice.

The skeptical-empirical argument. Some analysts argue that gerrymandering’s national seat effect is small and offsetting, and that geography and residential sorting drive much of the outcome.⁠⁶ The weak point is that the same research finds reduced competition and responsiveness, which are harms even when seats balance.

Unresolved questions

• After Callais, what kinds of evidence will satisfy the new “strong inference” of intentional discrimination standard, and how will lower courts apply it?.⁠⁵
• Will the 2025 to 2026 mid-decade redraws be followed by more, and does retaliation lead toward an equilibrium or an escalation?⁠^8,9
• How much do commissions increase competition, as opposed to changing who benefits? CRS notes the evidence is disputed⁠⁷
• Can state courts provide consistent standards after Moore v. Harper, or will protection depend on each state’s constitution and court composition?⁠⁴
• How should analysts separate deliberate gerrymandering from the effects of political geography in a given state?⁠⁶
• What would a national rule look like that both parties would accept?