An important new redistricting lawsuit in Wisconsin just cleared a major hurdle by surviving a motion for summary judgment and will now head to trial. The suit raises an argument that has been made many times before but without success: that election districts were drawn with the improper aim of maximizing one side's partisan advantage. In this case, the plaintiffs, a group of Democrats, have alleged that Wisconsin Republicans unfairly gerrymandered the state's legislative maps to benefit the GOP.
Every such case in the past that has made similar claims has ultimately failed because the Supreme Court (or more specifically, Justice Anthony Kennedy) has ruled that there's no manageable standard for judging when a partisan gerrymander is impermissible. But here, plaintiffs are relying on a new metric known as the "efficiency gap," a very compelling approach its creators describe thusly:
The efficiency gap is simply the difference between the parties’ respective wasted votes in an election, divided by the total number of votes cast. Wasted votes are ballots that don’t contribute to victory for candidates, and they come in two forms: lost votes cast for candidates who are defeated, and surplus votes cast for winning candidates but in excess of what they needed to prevail. When a party gerrymanders a state, it tries to maximize the wasted votes for the opposing party while minimizing its own, thus producing a large efficiency gap. In a state with perfect partisan symmetry, both parties would have the same number of wasted votes.
Put more concretely, every time a Republican legislator or member of Congress wins with 55 percent of the vote but a Democrat in the same state wins with 85 percent, far more votes are "wasted" on behalf of the Democrat—exactly what Republican cartographers want, and exactly what they’ve achieved in Wisconsin, where the GOP holds 62 percent of seats in the legislature even though Barack Obama carried the state twice.
Unlike other proposals, this test can be rigorously and empirically applied to any map, and now plaintiffs will have the chance to make their case in court. And should this dispute eventually reach the Supreme Court, it's quite possible that Justice Kennedy will finally find that the efficiency gap is a partisan gerrymandering standard he can love. But even if he doesn't, if a fifth liberal justice joins the court and finds this approach workable, it'll be a whole new day in redistricting jurisprudence, and a massive flood of lawsuits will follow.