Following the 2010 census, Wisconsin’s legislative districts were drawn by the Republicans after they swept state government. Democrats have been crying foul ever since, even though they planned on doing the same thing if they held on to the governor’s mansion and both houses of the state legislature. Not getting their way, the Democrats sued, and now Wisconsin’s legislative map (along with Maryland’s map) may be re-drawn by the U.S. Supreme Court.

The Wall Street Journal explains in an editorial why the Democrats’ case falls apart after they won the special election in the 10th Senate District on Tuesday.

Democrats say the victory could augur a wave election in November, and Republicans are right to be worried as voters sour on Mr. Trump’s tempestuous behavior. But we hope the Justices on the Supreme Court are paying attention because this Democratic rout contravenes the complaints Democrats made at the High Court last fall that Republicans have drawn legislative districts with such exactitude that Democrats can’t win.

In Gill v. Whitford, Wisconsin Democrats argued that partisan gerrymanders resulted in the GOP winning a disproportionate number of legislative seats relative to their statewide vote and thus prevented them from translating their votes into representation. They claim this violates equal protection under the Fourteenth Amendment and the First Amendment right to association.

But unlike gerrymandering by race, partisanship is neither a defined nor inhered identity. Politics can change on an individual and district-wide level from election to election. Democrats offered political-science mumbo-jumbo called the “efficiency gap” to supposedly prove discrimination. Under this model, any votes that don’t contribute to a candidate victory in a legislative race are deemed “wasted.” But Wisconsin’s results refute this since many of Ms. Schachtner’s 12,000 voters would have been considered wasted during prior Republican routs. A map’s efficiency gap will vary by election, so any standard would be arbitrary.

The Wall Street Journal also explains the threat from the Supreme Court deciding to redraw Wisconsin’s legislative map:

Democrats didn’t mind gerrymanders that helped them keep power in the House for 40 years before 1994, but now they want courts to help them overturn maps that help Republicans. The legal threat in Gill v. Whitford is that the Justices will make judges the arbiters of legislative redistricting that usurps the political branches and injects courts even deeper into partisan politics. This is anathema to the Constitution’s separation of powers.