Partisan gerrymandering can be unconstitutional—at least in theory. In the 1986 case of Davis v. Bandemer, the Supreme Court did not find reason to declare an unconstitutional gerrymander, but its ruling did state “that political gerrymandering cases are properly justiciable under the Equal Protection Clause.”

Despite that ruling, and despite regular rulings against racial gerrymanders over the past five decades, the Court hasn’t actually declared a single political district unconstitutional on the grounds that it disenfranchises voters by political party. In the 2004 Vieth v. Jubelirer case, Justice Antonin Scalia’s ruling on Pennsylvania congressional districts “concluded that political gerrymandering claims are nonjusticiable because no judicially discernible and manageable standards for adjudicating such claims exist.”

That ruling will be tested over the coming weeks, as the Court agreed Monday to review Gill v. Whitford, after a federal district court in November struck down Republican-drawn state assembly maps in Wisconsin on the grounds of partisan gerrymandering. In a story similar to other gerrymandering cases percolating in federal courts now, after grabbing control of the Wisconsin state legislature in 2010, Republicans used the Census-based decennial redistricting as an opportunity to dilute Democratic votes and solidify partisan advantage in the future. That advantage was so effective that at the time of the lower court’s ruling, scholars claimed Democrats would have to win 54 percent of the available votes to regain political control of the state.

There’s still an uphill battle for the Wisconsin plaintiffs and for opponents of partisan gerrymandering. In the Court’s order, the question of jurisdiction was postponed until a hearing on the merits of the case. That means the justices will have to determine if partisan gerrymandering is even justiciable. If they decide it’s not, that might be the death blow to future cases alleging partisan gerrymandering.

But there’s some hope for the plaintiffs yet. As Ian Millhiser at ThinkProgress notes, in the 2004 Vieth v. Jubelirer case, Justice Anthony Kennedy left the door open for a challenge. In response to Scalia’s holding that partisan gerrymanders are impossible to consider because there are no standards to measure how they affect constitutional rights and no useful objective tests to identify them (unlike racial gerrymanders, where discrete known factors are applied by the Court), Kennedy wrote that “if workable standards do emerge to measure these burdens … courts should be prepared to order relief.”

The lower court, at least, was swayed by one such standard. The University of Chicago professor Nicholas Stephanopoulos and the Public Policy Institute of California fellow Eric McGhee devised a way to measure the “efficiency gap” between parties. They measure “wasted” votes that occur either when a voter votes for a losing candidate or when a voter votes for a candidate who would have won anyways, which in turn captures the extent to which voters are “cracked” and placed in districts where their preferred candidates will never win or “packed” into hyper-concentrated districts. If one party has substantially more wasted voters and a lower efficiency than the other, then Stephanopoulos and McGhee claim that’s proof of an unconstitutional gerrymander.  The lower court found that claim compelling.

It’s unclear if the Supreme Court will find their formula equally compelling, but its decision will reverberate either way. North Carolina’s redrawn congressional districts now face review by federal courts as partisan gerrymanders after the original Republican-drawn maps were struck down by the Supreme Court. There are also ongoing lawsuits in Maryland and Pennsylvania over partisan gerrymandering.

The Court’s decision might impact those cases, but it could also have major effects on the future of redistricting. The 2020 Census isn’t far away, and Republicans in 2010 created a proof-of-concept for using hyper-partisan redistricting to amplify Democratic voter concentration and dominate local, state, and federal lawmaking bodies. Opponents—armed now with landmark analysis from Justice Kagan making it much easier to identify racial gerrymanders—will have real tools to fight this advanced gerrymandering, especially if the precedent in this case makes a partisan test available.

But if the Court takes the view that partisan gerrymandering is simply not actionable—or the more extreme view that it’s not any different from other partisan pieces of the political process under the Constitution—that decision will make it difficult to stop an increasingly sophisticated wave of hyper-partisan gerrymandering in 2021 and beyond.