Editor’s note: Earlier iterations of this post and podcast were first published on Sept. 28, before Wisconsin’s gerrymandering case was heard by the Supreme Court. Now that it has been heard by the court, we’ve updated both the post and podcast.

Is partisan gerrymandering constitutional? And if not, how is it to be measured? Those are the questions at the heart of one of the most consequential Supreme Court decisions of the coming year. How the court answers those questions in Gill v. Whitford has the potential to fundamentally change how we build our representative democracy.

This is the second installment of FiveThirtyEight’s podcast series “The Gerrymandering Project.” Throughout the series, we will travel around the country to explore the effects of gerrymandering and what reformers are doing to try to change the system. In our first episode, we laid out the basics of how we draw political boundaries and why it matters. You can listen to the new episode below or by subscribing to The Gerrymandering Project podcast feed.

The Case. After the 2010 midterm elections, the party in charge of Wisconsin’s government flipped. A Democratic Party-controlled State Assembly, Senate and governor’s office became controlled instead by the GOP. Soon after, it was time to redraw the district lines. Republicans came up with new maps that Democrats allege diluted their supporters’ voting power. The question for the court is whether the Republicans violated the Constitution by redrawing the district maps in their favor — a process known as partisan gerrymandering.

The Court. Conservative judges usually argue that it is not the court’s place to dictate the decision-making of a state legislature. Liberal judges maintain that the process has gotten out of hand to the point of violating the Constitution, and it is therefore the responsibility of the court to step in.

The decision is likely to come down to Justice Anthony Kennedy. He is a conservative judge, but his views on this matter don’t exactly align with either side of the aisle. In a 2004 opinion, he expressed alarm at the practice of extreme partisan gerrymandering but said the court should hold off on outlawing it. He also left the door open to ruling differently in the future, as long as lawyers provided a suitable way to measure when gerrymandering goes too far. He said that without that measurement, the court runs the risk of becoming too involved in a decision-making process that is legally mandated to state legislatures. Divining how justices will come down based on their behavior in oral arguments is always tricky business, but if history is any indication, things don’t look great for partisan gerrymandering. Kennedy did not direct a single question to the lawyer for the Wisconsin Democrats. A FiveThirtyEight analysis shows that Kennedy is more likely to side with a party when he stays silent during their arguments.

The Big Question. So, how exactly do you measure partisan gerrymandering? Reformers have scrambled to come up with an answer ever since Kennedy’s challenge. The solution presented in the current case proposes three questions to determine whether a map violates the Constitution:

Was the intent of the new map to benefit one party over the other? Does the map significantly discriminate against one party over a sustained period of time? The plaintiffs’ lawyers point to multiple ways to measure this in their case, but their primary measure has been the efficiency gap. We explain in full, using vodka tonics, in the podcast. Is there any reason other than partisan gerrymandering that one party is continuously at a disadvantage? For example: Are voters of one party naturally concentrated in a small number of districts?

To hear the story of how the case came to be and the arguments both sides are making, click on the play button above.

And while you wait for the next episode, be sure to subscribe to our Gerrymandering Project Facebook group. It’s a place to share your experiences with and opinions about gerrymandering. We’ll be having conversations there every week.