By MARK SHERMAN
Associated Press

WASHINGTON (AP) - The Supreme Court is wading into the thicket of partisan redistricting in a case from Wisconsin.

The justices on Monday said they will decide whether Republican lawmakers drew electoral districts so out of whack with the state's political breakdown that they violated the constitutional rights of Democratic voters.

It's the high court's first case on what's known as partisan gerrymandering in more than a decade, and the outcome could affect elections across the country.

Democrats hope a favorable decision will help them cut into GOP electoral majorities. Election law experts say the case is the best chance yet for the high court to put limits on what lawmakers may do to gain a partisan advantage in creating political district maps.

The case will be argued in the fall.

A three-judge court struck down Wisconsin's legislative districts in November and ordered new maps drawn in time for the 2018 elections. That work is proceeding.

The Constitution requires states to redo their political maps to reflect population changes identified in the once-a-decade census. The issue of gerrymandering - creating districts that often are oddly shaped and with the aim of benefiting one party - is centuries old. The term comes from a Massachusetts state Senate district that resembled a salamander and was approved in 1812 by Massachusetts Gov. Elbridge Gerry.

Both parties have sought the largest partisan edge when they control redistricting. Yet Democrats are more supportive of having courts rein in extreme districting plans, mainly because Republicans control more legislatures and drew districts after the 2010 census that enhanced their advantage in those states and in the House of Representatives.

The challengers to the Wisconsin districts said it is an extreme example of redistricting that has led to ever-increasing polarization in American politics because so few districts are genuinely competitive between the parties. In these safe seats, incumbents tend to be more concerned about primary challengers, so they try to appeal mostly to their party's base.

"Partisan gerrymandering of this kind is worse now than at any time in recent memory," said Paul Smith, who is representing the challengers to the GOP plan in Wisconsin.

Defenders of the Wisconsin plan have argued that the election results it produced are similar to those under earlier court-drawn maps. They said the federal court overstepped its bounds and judges should stay out of an inherently political exercise.

The justices should correct the lower court's "flawed analysis before it spreads to other jurisdictions and interferes with the states' fundamental political responsibilities," Texas Solicitor General Scott Keller wrote for 12 Republican-dominated states that are backing Wisconsin.

The issue has torn the court for decades. Some justices believe courts have no role to play in a matter best left to elected officials. Others say courts should step in. In 2004, Justice Anthony Kennedy staked out a position somewhere between those two views, saying courts could referee claims of excessively partisan redistricting, but only if they can find a workable way to do so. In that case and again in 2006, Kennedy didn't find one.

The Supreme Court has never struck down districts because of unfair partisan advantage, although it has intervened frequently in disputes over race and redistricting over the past 50 years.

Similar lawsuits are pending in Maryland, where Democrats dominate, and North Carolina, where Republicans have a huge edge in the congressional delegation and the state legislature.

Copyright 2017 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.