On Friday October 3, the U.S. Supreme Court will hear arguments in Gill v. Whitford, the court case concerning a voter redistricting plan created in 2011 for the Wisconsin State Assembly which used partisan gerrymandering. The question they will answer: Is partisan gerrymandering unconstitutional?
Why does this matter? Because it was partisan gerrymandering that enabled the party that won 47% of the vote for Wisconsin State Assembly in the 2012 election to take 61% of the Assembly seats. The Court’s decision is likely to shape American politics for years and perhaps decades to come.
Extreme gerrymandering is the subject of an excellent article in the September 3, 2017 edition of the New York Times Magazine: “Democracy vs. Math” by Emily Bazelon. The article focuses on two concepts of particular importance: partisan symmetry and efficiency gap.
The article describes how the 2011 Wisconsin Assembly map was struck down by a three-judge panel relying primarily on a metric called the efficiency gap, which measures “wasted votes.” Wasted votes are votes cast for a losing candidate, or votes exceeding the number a winning candidate needed to prevail. The efficiency gap is low when the number of wasted votes in a given election is similar for both parties, and it’s high when one side’s votes are wasted at a far greater rate, because its voters are concentrated densely (“packed”) or spread thinly (“cracked”).
The plaintiffs in Gill are asking the Supreme Court not to stop gerrymandering entirely but to agree that extreme gerrymandering can go too far. They argue for a baseline, proposed by Bernard Grofman of the University of California, Irvine, and Gary King of Harvard, who have studied redistricting for decades, for assessing how much gerrymandering is too much. Called partisan symmetry, it has widespread support among social scientists. Instead of dictating that a party with 46% of the vote must take 46% of the seats (that’s proportional representation, which the Supreme Court has rejected), partisan symmetry requires that if winning 46% of the popular vote gives the Republican party 60% of the congressional seats, then the Democratic Party should also win 60% of the seats if it wins 46% of the vote. It has been shown that the partisan symmetry standard can be logically derived from the equal treatment of individual voters, a right guaranteed by the 14th Amendment and Article 1 of the Constitution.
For more on the context and history of this highly consequential issue, I highly recommend that you read the NY Times Magazine article.