A voter casts a ballot behind a curtain at Smelser Town Hall in Georgetown, Wis., on Nov. 8. (Nicki Kohl/AP)

Federal judges struck down Wisconsin’s legislative map on Monday as illegally partisan, an unusual ruling that will require the Supreme Court to once again consider whether political gerrymandering violates the Constitution.

It is a question the court has addressed in the past without resolution. In its last attempt, Justice Antonin Scalia, who died in February, wrote that it was impossible for courts to come up with a test to decide when partisan line-drawing goes so far as to violate the rights of those who don’t belong to the party in power.

But the justices are divided, and they have not shut the door to the possibility that such violations could exist.

The three-judge panel in Wisconsin ruled 2 to 1 that such a violation occurred when the Republican assembly and Gov. Scott Walker (R) went to work drawing the state’s legislative districts in 2011. Judges in the majority said the Republicans drew lines to make it impossible for Democrats to receive their share of power.

The evidence presented in a four-day trial established that “one of the purposes of Act 43 was to secure Republican control of the Assembly under any likely future electoral scenario for the remainder of the decade, in other words to entrench the Republican Party in power,” wrote Judge Kenneth Ripple, who was nominated to the U.S. Court of Appeals for the 7th Circuit by President Ronald Reagan.

He was joined by U.S. District Judge Barbara Crabb, who was nominated by President Jimmy Carter. District Judge William Griesbach, chosen by President George W. Bush, dissented.

Such rulings on state redistricting plans go directly to the Supreme Court for review, without the usual stop at an appeals court. The Supreme Court must either affirm the judgment or schedule it for full briefing and decision.

Although justices are often called to decide whether legislative and congressional apportionment plans are unconstitutional because of racial gerrymandering, it has never struck down a plan because it was too partisan. Some justices take a “to-the-victor-goes-the-spoils” view of redistricting; others think it an unconstitutional problem.

In the court’s last look at the subject, Justice Anthony M. Kennedy ruled against the challengers at hand, but he noted that there could come a case where “the burdens and restrictions on groups or persons by reason of their views” would be so severe as to violate their First Amendment rights.

Those who believe partisan gerrymandering has contributed to a more divisive political climate have been working to get such a case to the Supreme Court. Similar lawsuits have been filed in Maryland and North Carolina.

Campaign Legal Center Executive Director J. Gerald Hebert, one of the lawyers in the case, said “the self-interested, unfair practice of partisan gerrymandering hurts our democracy. With this decision, partisan gerrymandering should come to an end in Wisconsin and is now on its way to extinction across the nation.”

The judicial panel said the map-drawing was biased against Democrats. It noted that in 2012, Democrats received 51.4 percent of the statewide vote and won 39 seats in the legislative assembly. Republicans won 52 percent in 2014, and that translated into 63 seats.