When states, counties, and towns redraw political districts, is it constitutional for them to include individuals who are ineligible to vote, such as noncitizens?

Or does that dilute the vote of eligible citizens and violate the one-person, one-vote standard that the U.S. Supreme Court established for all redistricting fifty years ago in Reynolds v. Sims (1964)?

The Supreme Court is set to finally decide this issue in Evenwel v. Abbott—something it has avoided for decades up until this year.

In Evenwel, two Texas voters claim that including noncitizens in the population used to draw their legislative districts violates the Equal Protection Clause. These voters were placed by the state legislature in senate districts whose voting populations deviate anywhere from 31 to 49 percent from the ideal population of a Texas senate district.

They argue that this disparity significantly dilutes their votes in comparison to those of voters who live in districts with large numbers of non-voters, particularly districts with large number of noncitizens, including illegal aliens who are not eligible to vote.

The basis for the one-person, one-vote standard is the Equal Protection Clause of the Fourteenth Amendment. Under the Supreme Court’s interpretation of the Fourteenth Amendment in Reynolds, states must draw districts “on a basis that will insure, as far as is practicable, that equal numbers of voters can vote for proportionally equal numbers of officials.”

This past summer, the Court accepted Evenwel for review. The Supreme Court’s 2015 term begins on October 5, although the date for oral arguments in Evenwel has not yet been set.

Sue Evenwel and Edward Pfenninger claim that their votes are worth roughly half those of voters in other districts. In other words, they argue that their districts were allotted the same number of senators as other districts that contained the same number of people but only half the number of eligible voters.

They are asking the Court to overturn a lower court decision that ruled against them and hold that this violates the one-person, one-vote standard.

In 2001, the Court declined to review another case out of Texas, Chen v. City of Houston, that raised this very same issue. In his dissent from the Court’s refusal to hear that case, Justice Clarence Thomas said that the Court had “left a critical variable in the [one-person, one-vote] requirement undefined.” The Court had “never determined the relevant ‘population’ that States and localities must equally distribute among their districts.”

In his dissent in another case in the Ninth Circuit Court of Appeals involving this issue, Judge Alex Kozinski pointed out that “at the core of one person one vote is the principle of electoral equality, not that of equality of representation.”

One issue that has been raised in this case is the accuracy and availability of population data on noncitizens who are ineligible to vote.

However, an amicus brief filed on behalf of Evenwel and Pfenninger by a number of demographers states that data about citizen voting-age population is readily available from the Census Bureau through the American Community Survey. That data is in widespread use by the U.S. Justice Department and other federal, state, and local government agencies.

On Tuesday, Sept. 15, the Center for Legal and Judicial Studies at The Heritage Foundation will kick off its Fall 2015 “Preserve the Constitution” series of events with a public discussion of the issues raised in the Evenwel case, including the possible political effect if the Court rules in favor of the challengers.

Speakers will include Andrew M. Grossman, a constitutional law expert at Baker Hostetler, who has filed an amicus brief in the case on behalf of Project 21: The National Leadership Network of Black Conservatives, and Sean Trende, the well-known senior elections analyst at RealClearPolitics. He is the co-author of the Almanac of American Politics 2014.

Join us in person or watch live over the Internet here.