On Monday, the Supreme Court of the United States issued a unanimous ruling in Evenwel v. Abbott, a voting rights case that dealt with how districts are drawn.

The opinion was written by Justice Ruth Bader Ginsburg, with Justices Clarence Thomas and Samuel Alito concurring. With the unanimous ruling, Justice Antonin Scalia’s death was not a direct factor in this decision, but since the Court left a major issue still open, the critical question of who will fill Scalia’s seat still looms.

When drawing district lines, who should be counted?

The case originated when two Texas residents, Sue Evenwel and Edward Pfenninger, challenged the state’s legislative redistricting, which currently includes the total population of the area, as is commonly done across the country. The plaintiffs argued in favor of counting only those residents who were actual voters to draw the districts.

As the U.S. Constitution already requires Congressional districts to be drawn based on total population, this case dealt only with state legislative districts.

Using voting population would, naturally, exclude a significant number of residents, including minors, prison inmates, convicted felons whose voting rights have not been restored, and non-citizens. Currently, because the population numbers are drawn from Census figures, all residents are counted, including non-citizens, whether they are legal residents or even illegal immigrants.

“Overwhelming majority” of states have used total population

Ginsburg’s opinion noted that using total population was the method used in the “overwhelming majority of cases,” citing as one of the “rare occasions” when only voters were counted a 1966 case allowing Hawaii to use this method because of Hawaii’s unique situation with its “substantial temporary military population.”

“Appellants have shown no reason for the Court to disturb this longstanding use of total population,” continued Ginsburg, describing the practice as “a well-functioning approach to districting that all 50 States and countless local jurisdictions have followed for decades, even centuries.”

Ginsburg found merit in including nonvoters in the districting process because elected representatives represent voters and nonvoters alike:

As the Framers of the Constitution and the Fourteenth Amendment comprehended, representatives serve all residents, not just those eligible or registered to vote. Nonvoters have an important stake in many policy debates—children, their parents, even their grandparents, for example, have a stake in a strong public-education system—and in receiving constituent services, such as help navigating public-benefits bureaucracies. 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.

Both Republicans and Democrats have benefited from counting non-voters.

Many liberal commentators took the position that drawing districts with voting population would benefit Republicans and rural districts, by shifting influence away from urban areas, which tend to lean Democratic. Caroline Frederickson, president of the liberal American Constitution Society, called the lawsuit an attempt to “dilute the political representation of minorities and children.”

However, counting non-voters can work to benefit Republicans, specifically when prisons are located in rural areas.

Back in 2011, Ross Ramsey at The Texas Tribune reported how large prison populations were used to bolster the numbers of the rural, Republican-leaning districts where the prisons were located. Ramsey described several rural districts with prisons where many of the inmates were Houston/Harris County residents before their incarceration.

If Texas had counted those inmates based on the address they had before being locked up instead of the addresses of their prisons, the nearly 30,000 incarcerated Houstonians around the state would have been enough to grant Harris County an additional legislative seat, which would have likely gone to a Democrat.

“Prison gerrymandering”

“Prison gerrymandering” has been a controversial practice for years. The Washington Times reported that Texas, Colorado, and Virginia were the top states using this practice after the 2000 Census, and noted a city council race in Iowa where only two votes were cast in a district that was “made up of 58 registered voters and 1,300 nonvoting prisoners at the Anamosa State Penitentiary.”

Lawsuits have been filed by liberal groups challenging this practice, including a suit brought by the ACLU in Jefferson County, Florida, where Jefferson Correctional Institute inmates counted for nearly half of the voting age population. According to Think Progress, Maryland,  New York, Delaware, Virginia, Massachusetts, Illinois, and California passed laws requiring or allowing states to count inmates at their last address before incarceration, and similar bills have been introduced in several other states.

Door cracked open for states to use voting population, but will they try?

Interestingly, the Court limited its ruling to rejecting the request to require Texas to using voting population to draw the maps, and stating that using total population was permissible under the Equal Protection Clause and the “one person, one vote” principle (as well as a widespread and long-accepted practice, as noted above).

Theoretically, this leaves the door open for a state to use voting population, but the Court did not resolve how they would rule. The State of Texas had argued that the Court should grant explicit permission to use voting population, and the Obama administration had wanted total population to be mandated, but the Court was persuaded by neither. Instead, the Court noted that they could not and would not rule on the issue of using voting population until they were presented with an actual case of a state using such a plan.

The end result is that states like Texas face a choice: they have been granted a green light to use total population to draw their state legislative districts, and may continue doing so. If they wish to switch to a voting population method, they will most likely face years of new litigation, as the stakes are high for both sides on this issue and the Court has deliberately refused to rule until they have an actual plan to review.

Follow Sarah Rumpf on Twitter: @rumpfshaker.