In 1962, Baker v. Carr established that the federal courts had jurisdiction to intervene in voter redistricting. The plaintiff lived in Tennessee, which had not redrawn its legislative districts since 1901. The state was required to redistrict every 10 years according to population, and the lack of redistricting diluted the representation of citizens in urban areas.
The chief question in Baker v. Carr was whether redistricting was a legal problem the courts could address proactively to correct abuses or a political problem. The state argued that it was a political issue, so the courts had no jurisdiction. The case proved one of the most exhausting in the Supreme Court's history, with the decision held over for re-argument because the court could not reach a majority decision. Justice Charles Evans Whittaker was so upset by the case, he finally recused himself from the decision, and the stress over the decision may have contributed to his early retirement from the Court.
The Baker decision forced not only Tennessee but many other states to redistrict in the 1960s, finally giving urban areas the representative weight their populations deserved. It also firmly established the concept of "one person, one vote," forcing states to ensure that districts were as evenly populated as possible.