WASHINGTON (Reuters) - The U.S. Supreme Court on Monday dealt a setback to election reformers by declining to use high-profile cases from Wisconsin and Maryland to curb the ability of state lawmakers to draw electoral districts purely for partisan advantage.

Sidestepping major rulings, the nine justices decided both cases on narrow legal grounds and put off perhaps until their next term, which begins in October, a more definitive ruling on whether courts can step in to limit the contentious practice known as partisan gerrymandering.

In the Wisconsin case, the court ruled 9-0 in favor of Republican legislators who drew state electoral districts that helped entrench their party in power, throwing out a lower court ruling that the map had deprived Democratic voters of their constitutional rights including equal protection under the law.

The ruling, authored by Chief Justice John Roberts, said the Democratic voters who sued to block the electoral map lacked the necessary legal standing because they challenged it statewide rather than focusing on individual districts.

The ruling makes it harder, but not impossible, for plaintiffs to challenge maps statewide. To do so, voters in every district in a state must show their own voting clout has been harmed.

In the Maryland case, the court’s unsigned opinion preserved a Democratic-drawn U.S. House of Representatives district challenged by Republican voters, but allowed the fight to continue in a lower court.

Election reformers in both parties had hoped the justices would rein in the intensified use of partisan gerrymandering, a practice in which the party that controls a state legislature uses the process of redrawing electoral districts after the U.S. census every decade to tighten its grip on power by diluting the influence of voters who tend to support the rival party.

Opponents have said partisan gerrymandering has begun to warp American democracy by muffling large segments of the electorate. Democrats in particular have accused Republicans of escalating partisan gerrymandering this decade, helping President Donald Trump’s party maintain control of the U.S. House of Representatives and state legislatures.

Critics have said gerrymandering has become more extreme through the use of precise voter data and computer modeling to devise electoral maps.

Journalists use umbrellas against the sun outside the U.S. Supreme Court on a day where the court handed a victory to Wisconsin Republicans who drew state electoral districts that helped entrench their party in power, but sidestepped a major ruling on whether parties have carte blanche to engage in the practice called partisan gerrymandering in Washington, U.S., June 18, 2018. REUTERS/Kevin Lamarque

NORTH CAROLINA CASE

Roberts said the court was leaving for another day whether judges have the power to remedy claims of unconstitutionally biased electoral maps. The justices could soon take up a challenge to Republican-drawn congressional districts in North Carolina that may give them another chance in their next term for a broader ruling on partisan gerrymandering.

The court’s four liberal justices indicated more sympathy toward hearing gerrymandering challenges. Justice Elena Kagan, joined by her fellow liberals, wrote that at its most extreme, partisan gerrymandering amounts to “rigging elections.”

“Courts have a critical role to play in curbing partisan gerrymandering,” Kagan said.

Gerrymandering usually involves packing voters who tend to favor a particular party in a small number of districts to diminish their statewide voting power while scattering others in districts in numbers too small to be a majority.

“The Supreme Court missed an opportunity today to lay down a firm marker as to when partisan gerrymandering is so extreme that it violates the constitutional rights of voters. But the court permitted lawsuits against unfair maps to continue,” said Dale Ho, a lawyer with the American Civil Liberties Union.

Democratic Party voters in Wisconsin sued state election officials in 2015 claiming a Republican-drawn legislative map was intended to discriminate against them for their political beliefs and create enduring Republican majorities.

While the state Democratic Party vowed to fight on, the state’s Republican attorney general, Brad Schimel, called the ruling a “win for the rule of law in Wisconsin.”

“In the future the court should go further and rein in the flood of political gerrymandering litigation that is clogging federal courts with dubious political science theories,” added the National Republican Redistricting Trust’s legal counsel, Jason Torchinsky.

The justices sent the Wisconsin case back to a lower court, though conservative Justices Clarence Thomas and Neil Gorsuch said they would have dismissed it outright.

University of Chicago Law School professor Nicholas Stephanopoulos, a lawyer for the plaintiffs, said the Democratic challengers will likely add voters from other Wisconsin districts to continue the case.

“I see today’s decision as a punt and as a complication for future litigants, but very far from a devastating defeat,” Stephanopoulos added.

Republican voters sued Maryland after the legislature in 2011 redrew boundaries for a largely rural congressional district north of Washington in a way that removed Republican-leaning areas and added Democratic-leaning areas. The five-page ruling did not resolve the merits of the plaintiffs’ claims.

Redistricting in most states is done by the party in power, though some states in the interest of fairness assign the task to independent commissions.