The case looks at Ohio's "purge policy", in which the state used maintenance lists to bar people from voting in elections if they had not voted in a two-year period or contacted a state voting agency for a six-year period.
A federal appeals court ruled for the state, concluding that roughly 7,500 OH voters - in a state that's perennially a presidential battleground - were wrongly purged from the list in the 2016 election. "What we're talking about are the best tools to implement that goal". Kennedy often swings a decision that splits the conservative and liberal-leaning justices.
The A. Philip Randolph Institute (APRI), a civil rights front, challenged the policy in court, citing two federal laws that prohibit states from purging voters "by reason of the person's failure to vote".
The National Association for the Advancement of Colored People (NAACP) said if the court sides with OH, it could unleash a wave of new state and local laws resulting in unnecessary purging and shrinking of voter rolls.
The case has taken on added importance because the parties have squared off over ballot access across the country. Republicans have argued that they are trying to promote ballot integrity and prevent voter fraud. Voters in OH who fail to vote in a federal election are issued a confirmation notice by mail.
States may remove voters who have died or moved to another state to maintain updated voter rolls.
Justice Elena Kagan countered that "proximate" does not mean "single", and that failure to vote substantially contributes to removal under Ohio's regime. If they don't return them and fail to vote for four more years, they're removed. If they do nothing, their names eventually fall off the list of registered voters.
OH is being backed in the case by 17 other mostly Republican states and the Trump administration.
Justice Sonia Sotomayor spoke at length about voter disenfranchisement, and noted that the state's policy disproportionately affected marginalized groups. That seems to be your position because it can be the only one.
"Places like Cleveland have very, very long lines", to vote, she observed, suggesting that other ways of determining whether voters have changed their address would be more effective than people's failure to vote.
A decision for OH would have widespread implications because it would fuel a broader effort to make it more hard and costly to vote, Ohio's opponents said.
In July, Secretary of State Jon Husted asked the high court to take up the case.
Opponents of the state's practice might ask, what about people who have been purged for being inactive and then are turned away when they decide to rejoin the democratic process?
Ho says says that Georgia, Montana, Oregon, West Virginia, Pennsylvania and Oklahoma also have a culling process that's triggered by inactivity, but Ohio's two-year trigger is the shortest of any state.
"Your argument really turns on the adequacy of the notice", Roberts said.
According to Perez, there's a possibility that the Supreme Court will hand down a narrow opinion saying Ohio's process in particular, by starting the process after just one federal election cycle without a vote cast, is too unreliable.
"My goal has always been to make OH a place where it's easy to vote and hard to cheat", he said.
The plaintiffs suing OH, represented by liberal advocacy group Demos and the American Civil Liberties Union, said that purging has become a powerful tool for voter suppression.
Mayor Joe Helle of Oak Harbor, Ohio, who was dropped from the rolls while serving in the U.S. Army, confronted Husted on the court's plaza.
They called Ohio's policy the most aggressive.