"One person, one vote" is deeply ingrained in the American psyche, but the concept isn't in the Constitution and it wasn't until the 1960s that the idea gained traction.
Retired Supreme Court Justice Sandra Day O'Connor remembers the days before the concept became common currency, as she told the producers of the documentary film "One Person, One Vote."
"I came from Greenlee County, Arizona, which never had a population of over 10,000 people," Justice O'Connor explains. "But both Maricopa County, with its two million people, and Greenlee County had the same number of members of the House of Representatives in Arizona and the same number of senators."
Justice O'Connor's former colleague, Justice Stephen Breyer, also recalls the days before "one person, one vote."
"When I grew up in San Francisco," Justice Breyer says in the documentary, "I knew perfectly well that the people in Northern California had probably more votes in the legislature than those in Southern California. And I would think, 'that's great!'"
The Supreme Court finally set out "one person, one vote" in a series of decisions known as the Apportionment Cases, and in 1964, in the case Reynolds v. Sims, the Justices decided that, under the Equal Protection Clause, state voting districts have to be equal in population.
The U.S. has changed a great deal since the Reynolds decision, though, and next week the Justices will decide whether to hear Lepak v. City of Irving, a case out of Texas that hinges on the question of whether "one person, one vote" means "one voter, one vote." As Richard Pildes, constitutional law professor at New York University, explains, Irving, Texas, is divided into six City Council districts, all equal in terms of population. One of the districts includes a significant immigrant population, however, rendering half of that district ineligible to vote. The eligible voters left therefore have more political power than those in the other districts.