The key vote, Justice Anthony Kennedy, gave little indication which way he'll side during the often lively session that saw a familiar partisan split.
At one point during arguments, he expressed concern with whether the challengers in the case had the legal right, or "standing," to bring their case to the court. But Kennedy, a conservative who has often sided with the four liberals on the bench, also seemed sympathetic to the idea that an extreme partisan gerrymander might violate First Amendment rights.
While the Supreme Court has a standard limiting the overreliance on race in map drawing except under the most limited circumstances, it has never been successful in developing a test concerning an overreliance on politics.
At issue are maps drawn in Wisconsin after the last census that Democrats say were drawn unconstitutionally to benefit Republicans. They argue the maps represent extreme partisan gerrymander and that they prevent fair and effective representation by diluting voters' influence and penalizing voters based on their political beliefs.
Lawyers for the state defend the maps, saying they are legitimate because legislators considered political implications as only one of several factors. They also argue it's not the job of the courts to write district lines, arguing that the challengers don't have the legal right to be in court and that the justices should decline to decide the issue and instead leave it to the political branches to decide.
A lower court ruled in favor of the challengers, setting out a standard to judge when partisan politics goes too far in map drawing.
It was clear that the liberal justices -- Elena Kagan, Ruth Bader Ginsburg, Stephen Breyer and Sonia Sotomayor -- thought such a challenge should go forward and a workable standard was possible.
At one point, Ginsburg asked, "what's really behind all of this?" and worried about the "precious right to vote." She continued, "if you can stack a legislature in this way, what incentive is there for a voter to exercise his vote?" Sotomayor asked how political gerrymander "helps our system of government." Kagan was deeply critical of the Wisconsin maps, saying they go "over pretty much every line you can name."
Chief Justice John Roberts led the charge for conservatives, including Justice Samuel Alito and Neil Gorsuch, arguing that the courts should not intervene in an issue that should be handled by the political branches.
Roberts worried about the reputation of the court and that if it were to get involved in issues considering partisan gerrymander it would make the court look political. "That is going to cause very serious harm to the status and the integrity of the decisions of this court in the eyes of the country."
He said the "main problem" for him was that if the court stepped in, other claims from across the country, "every one," would come to the court. And he questioned the social science relied upon by the challengers, calling it "gobbledygook." He narrowed in on the threshold issue of standing, saying he thought it was "arresting" that the challengers could bring a statewide challenge instead of district-by-district.
Gorsuch pushed on what standard the court could use to decide the cases -- "what is the formula?" he asked. Alito also chimed in on whether the court should take over from the political branches. "Is this the time," he asked, for us to "jump in?" Justice Clarence Thomas asked no questions, but he is expected to side with the conservatives.
When they were asked to take up the case last June, Wisconsin asked them to put on hold the lower court opinion that went against the state. The court agreed, but the liberal justices went out of their way to note that they would have denied the application for a stay. Over the summer, Ginsburg told an audience at a Duke Law school event that the Gill v. Whitford case was perhaps "the most important grant so far."
Although Kennedy did not tip his hand, he had no questions for a lawyer challenging Wisconsin.
"It's the most important case involving the structure of American politics in a generation," said Jeffrey Rosen, president of the National Constitution Center, at a recent event hosted by George Washington University Law School. The question: Are extreme partisan gerrymanders violations of either the equal protection clause or possibly the First Amendment?
In a 2004 partisan gerrymander case, conservatives on the court said they thought the issue should be handled by the political branches. But Kennedy was unwilling to bar all such future claims because he thought a workable standard to measure when there is an overreliance on politics might arise down the road.
"Partisan gerrymanders have become more common, more severe and more durable in their effects," Paul Smith, a lawyer for the Campaign Legal Center who is representing the challengers, argued in briefs. He said that partisan gerrymanders result in a violation of the "Equal Protection Clause by discriminating against the targeted party's voters" and preventing them from "fair and effective representation."
Part of the problem, he argued, is the fact that modern day technology has allowed better map-drawing that has "wrested power from voters." Using mapping software, census data and voting algorithms, he alleged the Republican map drawers diluted democratic votes by packing them into districts.
Erin Murphy, a lawyer at Bancroft who has filed an amicus brief on behalf of the Wisconsin State Senate and Wisconsin Assembly in support of the state, said that if the courts step into the battle it will transfer to judges a power that belongs with the political branches.
"Allowing claims like plaintiffs' to proceed would therefore wrest control over the districting process away from the state legislators to whom state constitutions assign the task, and hand it to federal judges, opportunistic plaintiffs and social scientists seeking to convert academic theories into constraints on the democratic process," she said.
A lower court ruled in favor of the challengers after conducting a trial in 2016. The court relied upon a three-part legal standard based on discriminatory intent, discriminatory effect and the justification for the law. The court concluded that the evidence established that one of the purposes of the redistricting plan -- Act 43 -- "was to secure Republican control of the Assembly under any likely future electoral scenario for the remainder of the decade, in other words to entrench the Republican Party in power."
Former President Barack Obama and former Attorney General Eric Holder have both taken up the cause. In a speech last July in Raleigh, North Carolina, Holder vowed to "ensure that after the next census in 2020 lines are drawn in a fair way -- not a partisan way -- to ensure that people's wishes are reflected in the candidates who are elected."
But the issue is not just one for Democrats. Arnold Schwarzenegger, the former Republican governor of California who sat in on Tuesday's arguments, called gerrymandering an "incumbent protection program" in a recent conference call.
A similar case is brewing in Maryland, but it was brought by Republicans.
And in a brief signed by Arizona Republican Sen. John McCain, lawyer Mark W. Moser asked the court to step in an adopt a standard that would block extreme partisan gerrymandering and stop special interest groups from infecting the map drawing process.
"Special interest groups, fueled by hidden funders with deep pockets and skin in the political game, are now focused on influencing redistricting," Moser wrote. "The payoff for these groups is obvious: By shaping the decennial redistricting process, special interest groups can affect the outcome of every congressional race in a state for the next decade."
CORRECTION: A previous version of this story misstated the results of the 2014 Wisconsin legislative election.