Last December the same conservative activists who persuaded the Supreme Court to gut the Voting Rights Act challenged the historic principle of “one, person, one vote.” They asked the Court to require states to draw districts based on eligible or registered voters, as opposed to total population, which had been the standard for more than 50 years. If that happened, millions of people, including children and non-citizens, would have been denied political representation. Districts would have become older, whiter, more conservative and more favorable to Republicans.

Today the Supreme Court rejected that challenge, upholding “one person, one vote” in a unanimous 8-0 decision. Justice Ruth Bader Ginsburg wrote the decision, saying that all people are entitled to equal representation under the law. “It remains beyond doubt that the principle of representational equality figured prominently in the decision to count people, whether or not they qualify as voters,” she wrote. (Justices Thomas and Alito concurred with the judgment but did not agree with its reasoning.)

Here’s the key part of her argument:

Adopting voter-eligible apportionment as constitutional command would upset a well-functioning approach to districting that all 50 States and countless local jurisdictions have long followed. As the Framers of the Constitution and the Fourteenth Amendment comprehended, representatives serve all residents, not just those eligible to vote. Nonvoters have an important stake in many policy debates and in receiving constituent services. By ensuring that each representative is subject to requests and suggestions from the same number of constituents, total-population apportionment promotes equitable and effective representation.

This is a major victory for voting rights, and a huge crisis averted. If states had been required to use current voting-age population instead of total population as the metric for drawing districts, as I previously reported, a staggering 55 percent of Latinos—those who are under 18 or non-citizens—would not have been counted, as well as 45 percent of Asian Americans and 30 percent of African Americans.

Yet this is still in many ways a bittersweet victory, given that the 2016 election is the first in 50 years without the full protections of the Voting Rights Act. We’re seeing the clear impact of that decision this year, with five-hour lines in Arizona, voters turned away from the polls by North Carolina’s voter-ID law, and 300,000 registered voters who could be disenfranchised in Wisconsin tomorrow.

Imagine if protecting voting rights were the norm, rather than the exception, before the Supreme Court. That’s why the future of the Court is the most important issue facing the country in 2016 and beyond.

Editor’s note: An earlier version of this article may have implied that the Court’s decision barred voter-eligible apportionment. In fact, though Justice Ginsburg’s opinion strongly endorsed total population apportionment as a “well-functioning approach” that “promotes equitable and effective representation,” the Court explicitly declined to “resolve” the question of whether states may use voter-eligible apportionment. While Justices Alito and Thomas concurred with the judgment, they disagreed with the opinion. The article has been updated to clarify these points.