Baker v. Carr (1962)

Tennessee's constitution required the legislature to reapportion its districts every ten years, but it had not done so since 1901, while the state's population shifted heavily to cities. By 1960 some rural districts had a fraction of the population of urban ones, so a minority of voters elected a majority of legislators. Charles Baker, a Shelby County voter, sued, arguing that the malapportionment denied him equal protection of the laws. Federal courts had long refused such cases, following Justice Felix Frankfurter's warning in Colegrove v. Green in 1946 that courts ought not to enter the political thicket.

On March 26, 1962, the Supreme Court ruled 6 to 2, in an opinion by Justice William Brennan, that the equal protection claim was justiciable and could be heard by federal courts. Brennan distinguished Guarantee Clause claims, which remained political questions, and set out six factors for identifying a nonjusticiable political question, including a textual commitment of the issue to another branch and a lack of judicially manageable standards. Justices Frankfurter and John Marshall Harlan II dissented. Chief Justice Earl Warren later called it the most important case of his tenure.

Baker led directly to the one person, one vote rule. In Wesberry v. Sanders in 1964 the Court required congressional districts of roughly equal population, and in Reynolds v. Sims the same year it applied the principle to both houses of state legislatures, forcing nearly every state to redraw its maps. The Court later declined to extend judicial review to partisan gerrymandering, holding in Rucho v. Common Cause in 2019 that such claims are political questions under Baker's factors. Supporters say Baker made representation fairer, while critics say it drew courts into political disputes.