Thornburg v. Gingles: Preconditions for Vote Dilution Claims

To bring a vote dilution claim under Section 2 of the Voting Rights Act, a plaintiff must satisfy three threshold requirements the Supreme Court set out in its 1986 decision Thornburg v. Gingles. The Thornburg v. Gingles preconditions are: the minority group is sufficiently large and geographically compact to form a majority in a single-member district; the minority group is politically cohesive; and the white majority votes as a bloc usually enough to defeat the minority’s preferred candidate. Meeting all three does not automatically win the case. It only opens the door to the broader “totality of circumstances” analysis that follows. And after the Supreme Court’s April 2026 decision in Louisiana v. Callais, each of these preconditions carries a heavier evidentiary burden than it did before.

Why the Test Exists

Section 2 prohibits any voting practice that gives minority voters less opportunity than other voters to participate in the political process and elect their preferred candidates. Before 1982, plaintiffs had to prove a state intended to discriminate. The 1982 amendments replaced that with a “results” test: discriminatory outcomes were enough, regardless of motive. The statute also expressly disclaimed any right to proportional representation.¹

Gingles was the Court’s first major test of the amended statute. The case challenged North Carolina’s use of multi-member legislative districts, which Black voters argued swamped their votes across large county-wide constituencies. The Court agreed, and in doing so built the three-part screen that governed Section 2 vote dilution claims for the next four decades.²

Precondition One: A Sufficiently Large and Geographically Compact Minority

The first step asks whether the minority group is large enough and concentrated enough to form a majority in a reasonably drawn single-member district. In the Court’s words, “the minority group must be able to demonstrate that it is sufficiently large and geographically compact to constitute a majority in a single-member district.”² Without that showing there is no geographic remedy a court could order. You cannot fix vote dilution by creating a new district if the minority population is too scattered to fill one.

In practice, plaintiffs satisfy this precondition by hiring demographers to draw an illustrative map showing a hypothetical district where the minority group exceeds 50 percent of the voting-age population. The proposed district cannot be bizarrely shaped or ignore traditional redistricting norms like keeping counties and communities intact. Courts evaluate compactness through both visual inspection and mathematical scores. Two common metrics are the Reock score, which compares a district’s area to the smallest circle that could contain it, and the Polsby-Popper score, which compares the district’s area to a circle with the same perimeter. Both produce a number between 0 and 1, with higher values indicating a more compact shape.

If the minority population is too dispersed or too small to cross 50 percent in a district that respects traditional boundaries, the claim fails at the starting gate.

The Strict 50 Percent Rule

The Supreme Court hardened this threshold in Bartlett v. Strickland (2009), holding that Section 2 does not protect “crossover” districts — districts where the minority group falls below 50 percent but could theoretically win by attracting some white voters.³ The first precondition relies on what the Court called an “objective, numerical test.” A group that cannot form an outright majority in a compact district cannot satisfy the first precondition, no matter how close it comes.

Precondition Two: Minority Political Cohesion

The second requirement shifts from geography to behavior. The minority group must vote cohesively for the same candidates. In the Court’s words, “the minority group must be able to show that it is politically cohesive.”² A minority population that splits its votes among many candidates does not have a clear collective preference, and no redistricting scheme can be blamed for the group’s inability to elect one.

Cohesion does not require unanimity. Courts look for a strong and consistent pattern across multiple elections, primary and general, where a clear majority of the minority group supports the same candidate. That pattern establishes that the group has distinct political interests capable of being represented if given the opportunity. When minority voters fracture unpredictably from race to race, the second precondition fails.

Precondition Three: Majority Bloc Voting

The third precondition targets the majority. Plaintiffs must show that white voters vote as a bloc “usually” enough to defeat the minority group’s preferred candidates.² This is the mechanism that actually causes dilution. A cohesive minority that should be able to elect its candidate gets consistently outvoted by a unified majority. Without that dynamic there is no structural barrier worth remedying.

The word “usually” carries real weight. An occasional defeat is not enough. Neither is a single election in which white voters rallied against a minority-preferred candidate. Courts look for a persistent pattern that effectively locks the minority out of representation. If white voters sometimes split and the minority’s preferred candidate wins a reasonable share of elections, the system is working well enough that Section 2 does not demand intervention.

Some divergence in candidate preferences between racial groups is expected and unremarkable. The question is whether the divergence is so extreme and durable that minority-preferred candidates almost never win under the existing district structure. Isolated successes, like winning an uncontested race, do not disprove the pattern.

How Polarized Voting Gets Proved

Because no one can see how individual voters mark their ballots, cohesion and bloc voting are established through statistical models that estimate group voting patterns from precinct-level data. The two standard techniques are ecological regression and ecological inference.⁴ Both examine the relationship between the racial composition of precincts and the vote totals for particular candidates.

Ecological regression, the older method, has significant weaknesses. It can produce logically impossible results, estimating for example that 115 percent of Black voters supported a given candidate. It also assumes voting patterns are uniform across precincts, which is rarely true. Ecological inference, developed by political scientist Gary King, incorporates mathematical bounds that prevent impossible estimates and provides precinct-level results rather than jurisdiction-wide averages. It also produces more reliable measures of uncertainty.

Expert witnesses typically present results from both methods and compare them, drawing on several election cycles. A single election can be anomalous; a pattern across many is far more persuasive. Which elections to analyze, and whether to weight contests that actually featured minority candidates, is often hotly contested between the parties.

What Happens After the Three Preconditions Are Met

Satisfying all three preconditions does not automatically establish a Section 2 violation. The court then evaluates the “totality of circumstances” to determine whether the political process is genuinely unequal for minority voters.¹ The analysis is guided by considerations drawn from the Senate Judiciary Committee report accompanying the 1982 amendments, commonly called the Senate Factors.⁵ They are not a checklist, and no specific number needs to point in the plaintiff’s favor.

The factors courts commonly examine include the jurisdiction’s history of official voting-related discrimination, the extent of racially polarized voting, the use of unusually large districts or majority-vote requirements that amplify bloc voting, whether minority members have been shut out of candidate slating, socioeconomic disparities in education, employment, and health that hinder political participation, racial appeals in campaigns, and the extent of minority electoral success. Courts may also consider whether elected officials are responsive to the minority community and whether the policy justifications for the challenged voting practice are legitimate or pretextual.⁵

In Johnson v. De Grandy (1994), the Supreme Court added that proportionality — whether the number of majority-minority districts roughly matches the minority group’s share of the population — is “always relevant” evidence but “never itself dispositive.” Rough proportionality is a strong defense but not immunity. A lack of proportionality suggests dilution but cannot prove it alone. The Court also rejected any requirement to “maximize” majority-minority districts.⁶

How Louisiana v. Callais Changed the Preconditions in 2026

The Gingles framework survived a direct challenge in Allen v. Milligan (2023), where the Court declined to require plaintiffs to prove their case against a “race-neutral benchmark” and reaffirmed decades of statutory precedent.⁷⁸ That reaffirmation held for three years.

On April 29, 2026, the Court issued Louisiana v. Callais. It did not formally abandon Gingles, but it restructured the framework so significantly that the dissent called Section 2 “all but a dead letter.”⁹ The case involved Louisiana’s congressional map, which a lower court had ordered redrawn to include a second majority-Black district. The majority struck down the remedial map as an unconstitutional racial gerrymander and used the case to rewrite the rules going forward.

Three changes matter most for the preconditions:

Illustrative maps cannot use race. Plaintiffs previously drew illustrative districts by identifying where minority populations lived and building a majority-minority district around them. Callais prohibits this. Proposed maps must now be drawn without race as a districting criterion and must satisfy all of the state’s legitimate redistricting goals, including partisan objectives.⁹
Racial voting must be separated from partisan voting. To satisfy the second and third preconditions, plaintiffs must now present a statistical analysis that controls for party affiliation. They must show racial bloc voting that cannot be explained by partisan preference alone. In heavily partisan areas where Black voters overwhelmingly prefer Democrats and white voters prefer Republicans, this requirement could make the second and third preconditions nearly impossible to satisfy.⁹
Totality of circumstances must focus on present-day intentional discrimination. Historical discrimination and current socioeconomic disparities characterized as “effects of societal discrimination” now deserve far less weight. The totality analysis must center on what the Fifteenth Amendment prohibits: current, intentional racial discrimination in voting.⁹

The practical effect is dramatic. The 1982 amendments were designed to replace an intent standard with a results standard. Callais effectively reinstates an intent requirement by demanding “a strong inference that the State intentionally drew its districts to afford minority voters less opportunity because of their race.” The majority framed the ruling as textual interpretation. Justice Kagan wrote in dissent that the decision “laid the groundwork for the largest reduction in minority representation since the era following Reconstruction,” warning that state legislatures could now dismantle existing majority-minority districts with little legal obstacle.⁹

A Boundary Worth Naming: Coalition Claims

Plaintiffs sometimes ask whether two or more distinct minority groups, such as Black and Latino voters, can combine populations to satisfy the first precondition. In Growe v. Emison (1993), the Supreme Court assumed without deciding that coalitions might be permissible but stressed that when distinct groups are aggregated, “proof of minority political cohesion is all the more essential.”¹⁰ Because the Court has never squarely decided the question, the federal circuits have split. The Fifth Circuit, which had allowed coalition claims for decades, reversed course in 2024, joining the Sixth Circuit in holding that Section 2 does not authorize aggregation. The Eleventh Circuit has suggested the opposite, though not as a formal holding. Whether a coalition claim is viable depends heavily on where the case is filed.

Where the Framework Stands

The three Gingles preconditions still frame every Section 2 vote dilution claim: a compact majority-minority district must be possible, the minority group must vote cohesively, and the white majority must usually vote as a bloc to defeat that group’s preferred candidates. What has changed is what plaintiffs must produce to satisfy each element. Drawing an illustrative map without considering race, disentangling racial voting from partisan voting, and proving present-day intentional discrimination are each formidable obstacles on their own. Combined, they mark a fundamental shift in how the Voting Rights Act operates in redistricting. Existing majority-minority districts are not automatically invalidated, but they face new vulnerability if state legislatures choose to redraw them, because the legal framework that produced many of them may no longer compel their preservation.

1
Office of the Law Revision Counsel. 52 USC 10301 – Denial or Abridgement of Right to Vote
2
Justia Law. Thornburg v. Gingles, 478 US 30 (1986)
3
Justia Law. Bartlett v. Strickland, 556 US 1 (2009)
4
Redistricting Data Hub. From RPV Data to RPV Analysis
5
U.S. Department of Justice. Section 2 Of The Voting Rights Act
6
Justia Law. Johnson v. De Grandy, 512 US 997 (1994)
7
Legal Information Institute. Allen v. Milligan
8
Supreme Court of the United States. Allen v. Milligan, No. 21-1086 (2023)
9
Supreme Court of the United States. Louisiana v. Callais, No. 24-109 (2026)
10
Justia Law. Growe v. Emison, 507 US 25 (1993)