Thornburg v. Gingles, 478 U.S. 30 (1986), was a United States Supreme Court case in which a unanimous Court found that "the legacy of official discrimination ... acted in concert with the multimember districting scheme to impair the ability of "cohesive groups of black voters to participate equally in the political process and to elect candidates of their choice." The ruling resulted in the invalidation of districts in the North Carolina General Assembly and led to more single-member districts in state legislatures.
Background
Legislative history
Section 2 of the Voting Rights Act of 1965 prohibits any jurisdiction from implementing a "voting qualification or prerequisite to voting, or standard, practice, or procedure ... in a manner which results in a denial or abridgement of the right ... to vote on account of race," color, or language minority status. The Supreme Court has allowed private plaintiffs to sue to enforce this prohibition. In City of Mobile v. Bolden (1980), the Supreme Court held that as originally enacted in 1965, Section 2 simply restated the Fifteenth Amendment and thus prohibited only those voting laws that were intentionally enacted or maintained for a discriminatory purpose. Congress responded by passing an amendment to the Voting Rights Act which President Ronald Reagan signed into law on June 29, 1982. Congress's amended Section 2 to create a "results" test, which prohibits any voting law that has a discriminatory effect irrespective of whether the law was intentionally enacted or maintained for a discriminatory purpose. The 1982 amendments provided that the results test does not guarantee protected minorities a right to proportional representation.
When determining whether a jurisdiction's election law violates this general prohibition, courts have relied on factors enumerated in the Senate Judiciary Committee report associated with the 1982 amendments ("Senate Factors"), including: The history of official discrimination in the jurisdiction that affects the right to vote; The degree to which voting in the jurisdiction is racially polarized; The extent of the jurisdiction's use of majority vote requirements, unusually large electoral districts, prohibitions on bullet voting, and other devices that tend to enhance the opportunity for voting discrimination; Whether minority candidates are denied access to the jurisdiction's candidate slating processes, if any; The extent to which the jurisdiction's minorities are discriminated against in socioeconomic areas, such as education, employment, and health; Whether overt or subtle racial appeals in campaigns exist; The extent to which minority candidates have won elections; The degree that elected officials are unresponsive to the concerns of the minority group; and Whether the policy justification for the challenged law is tenuous. The report indicates not all or a majority of these factors need to exist for an electoral device to result in discrimination, and it also indicates that this list is not exhaustive, allowing courts to consider additional evidence at their discretion.
Section 2 prohibits two types of discrimination: "vote denial", in which a person is denied the opportunity to cast a ballot or to have their vote properly counted, and "vote dilution", in which the strength or effectiveness of a person's vote is diminished. Most Section 2 litigation has concerned vote dilution, especially claims that a jurisdiction's redistricting plan or use of at-large/multimember elections prevents minority voters from casting sufficient votes to elect their preferred candidates. An at-large election can dilute the votes cast by minority voters by allowing a cohesive majority group to win every legislative seat in the jurisdiction. Redistricting plans can be gerrymandered to dilute votes cast by minorities by "packing" high numbers of minority voters into a small number of districts or "cracking" minority groups by placing small numbers of minority voters into a large number of districts.