Redistricting and Gerrymandering Explained

The Constitution requires an enumeration every ten years to divide House seats among the states by population. The House has been fixed at 435 members since 1913, and the Reapportionment Act of 1929 made the process automatic. After the 2020 census, Texas gained two seats and five other states gained one, while seven states lost one. Six states have only one seat and elect their member at large, so they do not draw congressional districts.

In Baker v. Carr in 1962 the Supreme Court held that redistricting disputes can be heard in federal court, and decisions in 1964 required districts of equal population, the principle of one person, one vote. Section 2 of the Voting Rights Act of 1965, as interpreted in Thornburg v. Gingles in 1986, required majority-minority districts in some circumstances, and the Court reaffirmed that framework in Allen v. Milligan in 2023. Shaw v. Reno in 1993 limited the use of race as the predominant factor. In Rucho v. Common Cause in 2019, the Court held that partisan gerrymandering claims are political questions federal courts cannot decide, leaving them to state courts and Congress.

A gerrymander works by wasting the other side's votes. Packing concentrates opposing voters into a few districts they win overwhelmingly, while cracking spreads them across many districts where they fall short. Map drawers use detailed voter data and software to test thousands of possible plans. Gerrymanders can protect incumbents, favor a party, or dilute or enhance the voting strength of racial groups, and the effects reduce the number of competitive seats.

Redistricting usually happens once a decade, but in 2025 the President urged Republican-led states to redraw maps before the 2026 midterms. Texas passed a new map in August 2025 aimed at gaining five seats, and the Supreme Court allowed it to be used. Missouri, North Carolina, Ohio, Florida, and Tennessee followed with maps favoring Republicans, though Missouri's was held up by a referendum petition. California voters responded by approving Proposition 50 in November 2025 to favor Democrats, a Utah court imposed a new map, and Virginia voters approved a Democratic-backed amendment that the state supreme court later struck down. Indiana's Senate rejected a new map. On April 29, 2026, in Louisiana v. Callais, the Court ruled 6 to 3 that Louisiana's second majority-Black district was an unconstitutional racial gerrymander and limited when Section 2 can justify race-based districts, after which Louisiana enacted a new map in May 2026 and the Supreme Court allowed Alabama to use its 2023 map for the 2026 elections.

Critics of gerrymandering argue that it lets politicians choose their voters, reduces competition, and deepens polarization, and they support independent commissions, state constitutional limits, or a federal ban. Others respond that commissions are not truly neutral, that map drawing is an inherently political task the Constitution assigns to legislatures, and that natural clustering of voters produces skewed results even without manipulation. Supporters of the Callais ruling say it moves the law toward race-neutral districting, while critics say it will reduce minority representation in Congress. Both parties have defended their 2025 and 2026 maps as responses to the other side.

In most states the legislature draws congressional and legislative maps as ordinary legislation, usually subject to the governor's veto. A growing number of states, including California, Arizona, Michigan, and Colorado, use independent citizen commissions, often created by ballot measures, while others use bipartisan or politician commissions. When legislatures deadlock or maps are struck down, state or federal courts may draw the lines. Some state constitutions require compact districts, respect for county lines, or partisan fairness.