The U.S. Supreme Court on Tuesday heard arguments in Evenwel v. Abbott, a case that challenges the fundamental component of representational democracy in how legislative districts are drawn.

Evenwel challenges “one person, one vote” in the drawing of state senate districts in Texas, arguing legislators should draw statewide districts based on the number of registered voters instead of the current method based off the total population as measured by the U.S. Census Bureau. If the plaintiffs succeed in their claim, the impact would be devastating for racial and social justice movements.

The conservative wing of the Roberts Court seems eager to accept the plaintiffs’ legal theory that by drawing legislative districts based on the total population rather than the number of registered voters, states violate the Equal Protection Clause of the 14th Amendment. To understand that, and the Evenwel challenge as a whole, it helps to know a little bit about the group behind it and the history of civil rights successes it hopes to undo.

Evenwel is the latest in a series of “representation” cases dreamed up by Edward Blum, director of the Project on Fair Representation, the organization behind Shelby County v. Holder, the 2013 case that gutted the Voting Rights Act. Blum is also behind Fisher v. University of Texas at Austin, the case challenging the race-based admissions policy at the University of Texas on the grounds that it discriminates against white students. The Roberts Court hears arguments in that case Wednesday.

Under the 14th Amendment, states are allocated seats in the House of Representatives by “counting the whole number of persons in each state.” States follow this process when determining their own statewide districts, thus counting the total number of people living in their state and carving up districts based on that tally, irrespective of the total number of registered voters in each district.

The plaintiffs in Evenwel argue that by counting children, documented and undocumented immigrants, prisoners, and other non-voters, Texas denies “eligible voters their fundamental right to an equal vote.”

They call it “the principle of ‘electoral equality.’”

Even the conservative U.S. Court of Appeals for the Fifth Circuit found that argument absurd, and dismissed the claim as “a theory never before accepted by the Supreme Court or any circuit court.”

In fact, the Supreme Court has quite explicitly ruled the exact opposite, during the last round of conservative political attacks on voting rights in the 1960s. This was most notable in Reynolds v. Sims, where the Supreme Court ruled that legislative districts had to be roughly equal in population rather than based on geographic area, as had been the practice, in part motivated by conservatives’ attempts to dilute the political power of urban areas compared to rural. “Legislators represent people, not trees or acres,” Chief Justice Earl Warren famously stated.

The Court issued the Sims decision in 1964. The following year Congress would pass the Voting Rights Act (VRA), explicitly prohibiting voting discrimination on the basis of race. For the first time in our country’s history, representational democracy was open for non-whites.

Conservatives have never stopped challenging the VRA since its passage.

Chief Justice John Roberts built his career in conservative jurisprudence working to undo the landmark civil rights law. It was almost possible to feel the smug in his smile when in 2013 the Court effectively gutted the law by telling Congress it had to go back and redesign the formula used to determine which states with a history of racial disenfranchisement would be subject to federal oversight.

But the principle of “one person, one vote” in terms of legislative apportionment is settled law. Or so the legal community thought.

Blum had tried twice before to bring a challenge to the “one person, one vote” principle and was turned away both times by the Roberts Court. The fact that on Tuesday the Court heard his argument, let alone seriously considered it, is itself victory for conservatives trying to advance “post-racial,” “All Lives Matter” rhetoric to upend civil rights advances, especially when it comes to voting rights. During the arguments, at least four, and maybe five, Supreme Court justices appeared willing to buy into the idea that democratic representation should be available only to registered voters, because to account for everyone who is not a registered voter is somehow discriminatory.

If they win, legislative districts would become older, whiter, more rural, and more conservative. Political power would shift from urban areas to rural areas. Our elected officials would be even older and whiter than they already are. Right now, people of color hold approximately 12 percent of all statewide elected offices. That number has been on the rise, thanks to decades of apportioning districts based on total population rather than registered voters, but a vote for the plaintiffs in Evenwel would change that upward progression of more diverse elected officials.

It would leave children, immigrants, most people who have committed felonies, and mentally ill people who do not have the legal capacity to vote effectively without a say in electoral representation, despite the fact that each of those populations is obviously impacted by the policy decisions their elected officials make.

If there is something that can save the “one person, one vote” principle from being cast aside by the Roberts Court, it is the fact that like conservatives’ ongoing crusade to upend health-care reform, the plaintiffs in Evenwel failed to offer any alternative method to apportioning districts that would work across the 50 states. That lack of a clear path away from more than 50 years of settled constitutional law may be what prevents the conservatives, and Justice Anthony Kennedy in particular, from issuing a sweeping ruling this term. Maybe.