The Thornburg v. Gingles case in 1985 was a significant U.S Supreme Court decision regarding voting rights, particularly for minority groups. The plaintiffs, black citizens of North Carolina, argued that the state's multi-member districting plan diluted their voting power and violated Section 2 of the Voting Rights Act of 1965. They claimed this system prevented them from electing representatives of their choice due to racially polarized voting patterns. The court ruled in favor of the plaintiffs with a majority opinion delivered by Justice Brennan; it established three preconditions for proving vote dilution under Section 2: (1) Minority group must be sufficiently large and geographically compact to constitute a majority in some reasonably configured legislative district; (2) Minority group must demonstrate political cohesiveness; (3) Majority votes as bloc usually to defeat minority-preferred candidate. This landmark ruling has had profound implications on redistricting plans across America since then.

In the dissenting opinion for Thornburg v. Gingles, Justice O'Connor argued that the majority's interpretation of Section 2 of the Voting Rights Act was overly broad and could potentially lead to racial gerrymandering. She contended that a minority group must demonstrate not only that it is politically cohesive and geographically compact but also show an established pattern of racially polarized voting in order to claim vote dilution under Section 2. Furthermore, she expressed concern about potential constitutional issues arising from race-based districting, cautioning against promoting a system where political identity is tied too closely with racial identity. In her view, this would risk reinforcing stereotypes rather than fostering genuine integration and equality.