Justices to look at Wis. partisan gerrymandering

Challengers say maps give one party advantage

WASHINGTON — The Supreme Court announced Monday that it would consider whether partisan gerrymandering violates the Constitution. The case could reshape U.S. politics.

In the past, the court has struck down election maps as racial gerrymanders that disadvantaged minority voters. But it has never disallowed a map on the ground that it was drawn to give an unfair advantage to a political party.

The challengers in the case say they have found a way to separate partisanship from the many other factors that influence how districts are drawn.

The case started when Republicans gained complete control of Wisconsin’s government in 2010 for the first time in more than 40 years. It was a redistricting year, and lawmakers promptly drew a map for the state Assembly that helped Republicans convert close vote totals into lopsided legislative majorities.

In 2012, Republicans won 48.6 percent of the statewide vote for Assembly candidates but captured 60 of the Assembly’s 99 seats. In 2014, 52 percent of the vote yielded 63 seats.

Last year, a divided three-judge U.S. District Court panel ruled that Republicans had gone too far. The map, Judge Kenneth F. Ripple wrote for the majority, “was designed to make it more difficult for Democrats, compared to Republicans, to translate their votes into seats.”

The new standard proposed by the challengers tries to measure the level of partisanship in legislative maps by counting “wasted votes.”

Packing many Democrats into a single district, for instance, wastes every Democratic vote beyond the bare majority needed to elect a Democratic candidate. Cracking, or spreading, Democratic voters across districts in which Republicans have small majorities wastes all of the Democratic votes when the Republican candidate wins.

In a 2015 article, Nicholas O. Stephanopoulos, a law professor at the University of Chicago and a lawyer for the plaintiffs, and Eric McGhee devised a formula to measure partisanship. The difference between the two parties’ wasted votes, divided by the total number of votes cast, yields an efficiency gap, they wrote.

In a world of perfect nonpartisanship, there would be no gap. The gap in Wisconsin was 13.3 percent in 2012 and 9.6 percent in 2014, according to the formula. The Wisconsin voters who sued to challenge the Assembly map argued that gaps over 7 percent violated the Constitution.