In a major victory for those who believe that courts should be in the business of policing redistricting plans that give partisan advantage to one party or another, a three-judge court has ruled 2-1 that the Wisconsin assembly districts drawn by the WI Republican legislature are an unconstitutional partisan gerrymander. There’s still more to do in the case—namely figure out the correct remedy—but this is a case that will be headed directly to the Supreme Court, where its fate might depend upon who President-elect Trump nominates to the Supreme Court.

Here’s the quick overview for those who need to get up to speed:

The state of play in partisan gerrymandering claims is a crazy one: thanks to the position of Justice Kennedy in the Supreme Court (in the Vieth case and others), partisan gerrymandering claims are “justiciable” (meaning the courthouse door is open to raising the claims), but every usual standard that plaintiffs have raised to try to prove a partisan gerrymander has been rejected by Justice Kennedy. Kennedy’s message in essence is: keep trying to come up with a judicially manageable standard that separates permissible from impermissible consideration of party in redistricting. So if you are a plaintiff bringing such suits, you have to raise something different from what’s already been raised as well as something which could well attract the votes of five Justices, including Justice Kennedy. Plaintiffs in the Wisconsin case have raised a kind of partisan symmetry argument, one which J. Kennedy did not completely close the door to in earlier cases. In particular, plaintiffs in this case are relying on the “efficiency gap” measurement set forth in Nicholas O. Stephanopoulos & Eric M. McGhee, Partisan Gerrymandering and the Efficiency Gap, 82 U. Chi. L. Rev. 831 (2015).

In today’s opinion, the majority looks to the efficiency gap as evidence of illegal partisan entrenchment, but it alone does not prove the case. Here is how the majority sets forth the elements of the cause of action:

As our description of the case law reveals, the law governing political gerrymandering, still in its incipient stages, is in a state of considerable flux. We must, however, accept that situation and seek in these authorities a solution to the case before us. Therefore, while not discounting the difficulty of the task before us, we now identify the guideposts available to us. We begin with a principle that is beyond dispute. State legislative apportionment is the prerogative and therefore a duty of the political branches of the state government. We must “recognize[] the delicacy of intruding on this most political of legislative functions.” Bandemer, 478 U.S. at 143.166 We also know that we cannot rely on the simple finding “that political classifications were applied.” Vieth, 541 U.S. at 307 (Kennedy, J., concurring in the judgment). Similarly, “the mere lack of proportional representation will not be sufficient to prove unconstitutional discrimination.” Bandemer, 478 U.S. at 132 (plurality opinion). It is clear that the First Amendment and the Equal Protection Clause protect a citizen against state discrimination as to the weight of his or her vote when that discrimination is based on the political preferences of the voter.167 This principle applies not simply to disparities in raw population, but also to other aspects of districting that “operate to minimize or cancel out the voting strength of racial or political elements of the voting population.” Fortson, 379 U.S. at 439. Specifically, apportionment plans that “invidiously minimize[]” the voting strength of “political groups” “may be vulnerable” to constitutional challenges, Gaffney, 412 U.S. at 754, because “each political group in a State should have the same chance to elect representatives of its choice as any other political group,” Bandemer, 478 U.S. at 124. We conclude, therefore, that the First Amendment and the Equal Protection clause prohibit a redistricting scheme which (1) is intended to place a severe impediment on the effectiveness of the votes of individual citizens on the basis of their political affiliation, (2) has that effect, and (3) cannot be justified on other, legitimate legislative grounds.

There is a lot of detail and technical specifics I haven’t worked through yet, but this is the essence of the court’s analysis. To the dissenting judge, Judge Griesbach, plaintiffs’ claims are no different from the claims in earlier cases in which the Supreme Court has found there is no manageable standard for separating permissible information about partisan affiliation from unconstitutional partisan gerrymandering:

The Supreme Court heard this same story in 1986. It was unmoved. In 2004 the Court rejected a similar claim, and the reasons the Justices cited only twelve years ago apply with equal force now. What made this case different is the Plaintiffs’ claim that they had discovered the holy grail of election law jurisprudence—the long sought after “judicially discernable and manageable standard” by which political gerrymander cases are to be decided. Yet, even the majority has declined Plaintiffs’ request that the efficiency gap standard be adopted as the presumptive test, choosing instead to use it merely as corroborative evidence of its own entrenchment test. Slip Op. at 86. As I have attempted to show above, however, the majority’s entrenchment test offers no improvement over the tests that have already been rejected by the Supreme Court. And the efficiency gap theory on which the Plaintiffs founded their case fatally relies on premises the courts have already rejected, including proportional representation, and it suffers from a number of practical problems as well. Simply put, I do not believe the Supreme Court would direct courts to meddle in a state districting plan when that plan adequately hews to traditional and legitimate districting principles; contains no “gerrymander,” as traditionally understood; and when the plan only modestly extends the map-drawing party’s electoral advantage beyond what would exist naturally. This is particularly true given that the gerrymandering party very likely would have won both elections conducted under the challenged plan even without gerrymandering. Under these circumstances, and given the Justices’ reluctance to review gerrymandering claims, the Plaintiffs’ theory does not persuade me that a majority of the Supreme Court would find an unconstitutional gerrymander in this case. Accordingly, I would find in favor of the Defendants and therefore respectfully dissent.

Because this case comes directly from a three-judge court, it goes on direct appeal to the Supreme Court where an opinion not to hear the case (and to simply affirm) means the lower court got the right result. That fact (as I explain in this Stanford Law Review piece) makes it extremely likely the Court will agree to hear this case on the merits—or at least hold it while it considers another one of these cases (there is one working its way up from Maryland and one from North Carolina—it is not clear to me which one gets there first).

So what happens when this case gets to the Supreme Court? There are four votes (the four liberals) likely to embrace the result in this case, if not necessarily the precise reasoning. There are three Justices (CJ Roberts, and Justices Alito and Thomas) likely to reject the claim in this case as non-justiciable. So to get to a fifth vote there are two possibilities: Justice Kennedy likes what he sees here, in contrast to the other cases where he has waited and rejected other standards, or a new Ninth Justice appointed by President Trump votes for it. How likely is that? Well Trump has promised to appoint someone like Justice Scalia, if that new Justice votes like Scalia, it’s not likely at all. But this is not an issue that necessarily breaks along party lines, and so we will have to see how things go.

So bottom line: this is a big victory for those who want to see courts rein in partisan gerrymandering. But it is anybody’s guess what happens to this when it gets to the Supreme Court.

[This post has been updated.]