The Supreme Court might rule on a case to limit gerrymandering — and that’s a big deal, Sarah Kliff, Ezra Klein, and Matt Yglesias concluded on the October 10 episode of The Weeds, which also discussed the Children’s Health Insurance Program and a white paper from a Nobel Prize winner.

The background of the case in the Supreme Court, Gill v. Whitford, is this: In 2010, Wisconsin’s map of electoral districts was redrawn by the Republican state legislature. In 2012, Republican candidates in the statehouse won 48 percent of the vote but 60 of the 99 legislative seats. Democrats won 51 percent that year but only received 39 seats.

“Republicans had figured out a way to lock in a legislative majority basically no matter what happens. You could have a democratic wave bigger than you’d had in 40 years and Republicans would keep the state legislature,” Ezra said.

Ezra explains that in the past, the Supreme Court has ruled on gerrymandering but never could come up with a solution to the problem. This case seems to be different, he says, because, “It does seem like for the first time that there is a manageable standard. It looks like there might be a 5-4 majority for it, and this is in front of the Supreme Court in a pretty robust way.”

The solution social scientists have drawn up is to keep the “efficiency gap” at or below seven percentage points As Ezra explains:

Eric McGee, a political scientist who works at the Public Policy Institute of California, invents this new standard for measuring partisan gerrymanders called the efficiency gap. You can gerrymander in two ways: You can do what is called “packing,” where you try to pack all of a political party’s voters into one district — so the idea there is, say Democrats are packed into a district where the Democratic candidate always wins by 85 percent, but that means that all of those Democrats are not available to vote in other congressional districts. Or you can do “cracking,” where you are spreading your own people very thin. Every one of your candidates wins by, like, 54 percent, and you get a very efficient situation. Basically what the efficiency gap is doing is it tests how many votes are wasted. So how many votes you are having over a candidate’s winning margin in all districts and then compares the wasted vote count of Republicans and Democrats. SARAH: Well, it is also counting the number of votes wasted in districts you lost, right? You are comparing those two against each other? EZRA: Right, all wasted votes everywhere, and you are comparing them against each other. You are seeing if there is a huge difference in wasted votes across groups. I want to give an example here, and we actually had one of the plaintiff’s lawyers write this up at Vox. He writes, “take a state with five districts. You have two won easily by Democrats, 76 percent to 24 percent, and then three other districts that were won narrowly by Republicans, so 59 percent to 41 percent. Democrats wasted 26 percent of the vote in the two districts that they won and then Republicans wasted 24 percent of the vote in the two districts they lost and 9 percent in the three districts they win.” So if you run the math on all this, the Democrats get 55 percent of the statewide vote but just 40 percent of the seats, which means there is a pro-Republican efficiency gap of 20 percent. So what the plaintiffs are alleging is that there is now a way to measure clearly whether somewhere has been partisan gerrymandered too aggressively. They are not saying there should be no level of partisan gerrymandering, but that the top efficiency gap that the Supreme Court should be willing to tolerate is plus 7 percentage points.

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