The law of redistricting has been built case by case at the Supreme Court, and the famous gerrymandering cases most often cited today form a fairly tight sequence: Baker v. Carr opened federal courts to redistricting disputes in 1962, Wesberry and Reynolds imposed equal population in 1964, Thornburg v. Gingles set the test for racial vote dilution in 1986, Shaw v. Reno limited how far states can go in drawing districts by race in 1993, Shelby County v. Holder ended federal preclearance in 2013, Rucho v. Common Cause shut federal courts out of partisan gerrymandering claims in 2019, Moore v. Harper preserved state court review in 2023, and Allen v. Milligan and Alexander v. South Carolina NAACP set the current terms of racial redistricting fights in 2023 and 2024.
Baker v. Carr (1962)
For most of the twentieth century, federal courts refused to touch redistricting. Judges treated map-drawing as a “political question” reserved to legislatures. Tennessee had not redrawn its legislative districts since 1901 despite a state constitutional requirement to do so every ten years, and sixty years of migration to the cities meant a rural vote counted for several urban ones. Charles Baker, a Shelby County voter, argued the disparity violated the Equal Protection Clause.1Justia. Baker v. Carr
By 6-2, the Court held that redistricting challenges under the Equal Protection Clause are justiciable. Justice Brennan’s opinion did not say Tennessee’s map was unconstitutional. It said federal courts could hear the case. The ruling also formalized the political question doctrine into a six-factor test, including whether judicially manageable standards exist, a framework that would resurface decades later when the Court confronted partisan gerrymandering.2Legal Information Institute. Baker v. Carr (1962)
Wesberry v. Sanders and Reynolds v. Sims (1964)
Two decisions the following term filled in what equal representation actually required.
In Wesberry v. Sanders, the Court struck down Georgia’s congressional map, where the Atlanta-anchored Fifth District held two to three times the population of some rural districts. The Court held that Article I, Section 2, which requires representatives to be chosen “by the People,” demands that congressional districts contain roughly equal populations. The opinion set “equal representation for equal numbers of people” as the goal for the House, without requiring mathematical precision.3Justia. Wesberry v. Sanders, 376 U.S. 1 (1964)
Because Wesberry rests on Article I rather than the Fourteenth Amendment, the population-equality standard for congressional districts is stricter than the state legislative one. Courts have historically tolerated almost no deviation.
Reynolds v. Sims applied the same principle to state legislatures. Alabama still used a 1901 apportionment and argued its senate could mirror the U.S. Senate by giving each county equal representation. Chief Justice Warren rejected that analogy, writing that “legislators represent people, not trees or acres,” and held that both chambers of a state legislature must be apportioned by population under the Equal Protection Clause.4Justia U.S. Supreme Court Center. Reynolds v. Sims, 377 U.S. 533 (1964)
The practical rule that developed for state legislative districts allows more flexibility. A total population deviation under ten percent is generally acceptable, though smaller deviations can still be struck down if they reflect illegitimate line-drawing. Deviations above ten percent are presumptively suspect, and the state must justify them.
Thornburg v. Gingles (1986)
Population equality alone does not stop mapmakers from neutralizing minority voting power by packing minority voters into one district or fracturing them across several. Section 2 of the Voting Rights Act prohibits any voting practice that results in denying or reducing a citizen’s right to vote on account of race. After a 1982 amendment, plaintiffs no longer had to prove discriminatory intent. They needed to show that, under the totality of circumstances, minority voters had less opportunity than other voters to elect representatives of their choice.5Office of the Law Revision Counsel. 52 USC 10301 – Denial or Abridgement of Right to Vote on Account of Race
Thornburg v. Gingles turned Section 2 into a workable test. A plaintiff must first clear three preconditions:
- The minority group must be sufficiently large and geographically compact to form a majority in a single district.
- The group must be politically cohesive, meaning its members tend to support the same candidates.
- The white majority must vote as a bloc in a way that usually defeats the minority group’s preferred candidates.
Clearing all three does not by itself prove a violation. Courts then weigh additional factors, including the jurisdiction’s history of voting-related discrimination, the degree of racially polarized voting, and whether minority candidates have won office there.6Justia. Thornburg v. Gingles, 478 U.S. 30 (1986)7United States Department of Justice. Section 2 Of The Voting Rights Act
Gingles remains the backbone of redistricting litigation nearly forty years later. Every packing-or-fracturing case starts with those three questions.
Shaw v. Reno (1993)
Efforts to comply with the Voting Rights Act sometimes produced maps with constitutional problems of their own. North Carolina’s 12th Congressional District, drawn after the 1990 census, ran roughly 160 miles along Interstate 85, at points no wider than the highway itself. One state legislator quipped that driving down I-85 with both car doors open would “kill most of the people in the district.”8Justia. Shaw v. Reno, 509 U.S. 630 (1993)
Five residents challenged the district as an attempt to sort voters by race. The Court held that a redistricting plan so irrational on its face that it is “unexplainable on grounds other than race” triggers strict scrutiny under the Equal Protection Clause. The state must then show the racial classification serves a compelling governmental interest and is narrowly tailored to achieve it.
Shaw created a tension mapmakers still navigate. The Voting Rights Act may require creating districts where minority voters can elect their candidates of choice, but the Equal Protection Clause forbids making race the dominant factor in drawing those lines. States have to thread that needle.
Shelby County v. Holder (2013)
For decades, the strongest federal tool against discriminatory redistricting was prevention rather than after-the-fact litigation. Section 5 of the Voting Rights Act required states and localities with a history of discrimination to get federal approval, known as preclearance, before changing voting laws or district maps. Section 4 defined which jurisdictions were covered using a formula based on historical voter registration and turnout data.
In 2013, the Court struck down the coverage formula as unconstitutional. Chief Justice Roberts wrote that the formula, last updated in 1975, relied on decades-old data that no longer reflected current conditions. Section 5 remains on the books but inoperable without a valid formula, and Congress has not enacted a new one.9Justia. Shelby County v. Holder, 570 U.S. 529 (2013)
The 2020 redistricting cycle was the first in over sixty years conducted without preclearance in force. Section 2 lawsuits are still available, but they come after maps take effect and can take years to resolve. Under preclearance, the burden was on the state to prove its maps were clean before using them. Now, disputed maps can govern elections for a full cycle before a court orders them redrawn.
Vieth, Gill, and Rucho: The Federal Courts Step Out
Racial gerrymandering has a constitutional framework. Partisan gerrymandering has been much harder for courts, and after decades of trying, the Supreme Court gave up on finding a federal judicial answer.
Vieth v. Jubelirer (2004)
Pennsylvania’s 2002 congressional map was drawn with surgical partisan precision. A plurality of four justices concluded that partisan gerrymandering claims are inherently nonjusticiable because no workable standard exists for identifying when partisanship crosses the constitutional line. Justice Kennedy declined to join that conclusion in full. He voted to dismiss the specific challenge but wrote that courts should not foreclose the possibility that a manageable standard might emerge, perhaps under the First Amendment.10Supreme Court of the United States. Vieth v. Jubelirer, 541 U.S. 267 (2004)
Kennedy’s concurrence kept the question alive for fifteen more years while reformers and political scientists developed quantitative metrics designed to give courts the standard he had called for.
Gill v. Whitford (2018)
Wisconsin’s state legislative maps became the next major test. Plaintiffs presented the “efficiency gap,” a metric comparing each party’s wasted votes across all districts, as the elusive standard. The Court sidestepped the merits. Writing for a unanimous Court on standing, Chief Justice Roberts held that voters challenging gerrymandered maps must show harm in their own specific district. A generalized grievance that the statewide map is unfair does not satisfy Article III.11Supreme Court of the United States. Gill v. Whitford (2018)
Rucho v. Common Cause (2019)
The following term paired a challenge to North Carolina’s Republican-favoring congressional map with a challenge to Maryland’s Democratic-favoring map. The Court acknowledged that excessive partisan gerrymandering is “incompatible with democratic principles,” then held 5-4 that partisan gerrymandering claims present political questions beyond the reach of federal courts.12Supreme Court of the United States. Rucho v. Common Cause, 588 U.S. ___ (2019)
The core problem, in the majority’s view, was the one Kennedy had flagged in Vieth: the Constitution provides no standard for deciding how much partisanship is too much. Every map reflects some political judgment, and without a constitutional baseline federal courts have no principled way to draw the line. The majority pointed to state courts, state constitutions, independent redistricting commissions, and Congress as the proper venues.
Moore v. Harper (2023)
Rucho did not say partisan gerrymandering is acceptable. It said the federal Constitution offers no remedy. State constitutions often contain their own protections, and after 2019 state courts became the primary forum for partisan gerrymandering claims. Several state courts struck down congressional or legislative maps under state constitutional provisions during the 2020 cycle.
Opponents of state court intervention pushed the “independent state legislature theory,” which argued that because the federal Constitution assigns state legislatures the power to set rules for federal elections, state courts cannot review those rules under state constitutions. If adopted, the theory would have stripped state courts of authority to strike down gerrymandered congressional maps.
The Court rejected it 6-3. Chief Justice Roberts wrote that when state legislatures draw congressional districts, they remain subject to ordinary state judicial review. The Elections Clause does not insulate legislatures from their own state constitutions.13Supreme Court of the United States. Moore v. Harper (2023)
Moore preserved the most viable path for challenging partisan gerrymanders after Rucho. It also confirmed that the growing number of states using independent redistricting commissions operate on solid constitutional footing. Roughly a dozen states now use commissions for congressional redistricting, with more using them for state legislative maps.
Allen v. Milligan and Alexander v. South Carolina NAACP
The two most recent redistricting decisions pull in opposite directions and show how unsettled this area of law remains.
Allen v. Milligan (2023)
Alabama’s 2020 congressional map contained one majority-Black district out of seven, though Black residents made up roughly 27 percent of the state’s population. Plaintiffs argued a second majority-Black district could be drawn and that failing to do so violated Section 2. Alabama asked the Court to rework the Gingles framework and make it harder to challenge maps on racial grounds.
The Court declined 5-4. The majority upheld the lower court’s finding that plaintiffs had satisfied all three Gingles preconditions and affirmed that Alabama’s map likely violated Section 2. The opinion explicitly refused to “revise and reformulate” the test that had been the baseline for Section 2 cases for decades.14Justia. Allen v. Milligan, 599 U.S. ___ (2023)
Alexander v. South Carolina NAACP (2024)
One term later, the Court made racial gerrymandering claims harder to win. South Carolina redrew a Charleston-area congressional district after the 2020 census, shifting about 30,000 Black residents out and replacing them with white residents. The lower court found race had predominated. The Supreme Court reversed 6-3, holding that the finding was clearly erroneous because plaintiffs had not proven that race, rather than partisanship, drove the changes.15Supreme Court of the United States. Alexander v. South Carolina State Conference of the NAACP (2024)
The opinion emphasized that courts must start with a presumption the legislature acted in good faith. When evidence could plausibly support either racial or partisan motivations, the tie goes to the legislature. A plaintiff must “disentangle race from politics” and prove that race was the criterion the state would not compromise on. If partisan considerations alone could explain the district’s shape, the claim fails.
The two cases combined leave a narrow path. After Rucho, federal courts will not review maps for partisan gerrymandering. After Alexander, legislatures can defend against racial gerrymandering claims by arguing the decisions were partisan rather than racial. Where race and party affiliation are closely correlated, that defense is often available, and proving a racial gerrymandering claim becomes substantially harder. This is the ground on which the next round of redistricting cases will be fought.