(Ricky Carioti/The Washington Post)

A decades-long effort to keep politicians from drawing district lines that entrench themselves and their parties in power faltered Monday at the Supreme Court, as justices sidestepped the question of when extreme partisan gerrymandering is unconstitutional.

In considering a Republican-drawn map from Wisconsin and a Democratic effort in Maryland, the court had raised the possibility of producing a landmark change in the way the nation’s elections are conducted.

The justices left the door open for future challenges to partisan gerrymanders. But as a result of Monday’s technical resolutions, both states’ maps will be intact for the 2018 elections, and the status quo remains.

The ruling indicates that the court’s pivotal justice, Anthony M. Kennedy, was not persuaded by the challengers that they had presented a way for courts to determine when partisan efforts so infect a state’s political maps that they violate the Constitution.

“Today’s decision is yet another delay in providing voters with the power they deserve in our democracy,” said Chris Carson, president of the League of Women Voters of the United States. “Partisan gerrymandering is distorting and undermining our representative democracy, giving politicians the power to choose their voters, instead of giving voters the power to choose their politicians.”

While the court regularly polices state redistricting efforts that can harm racial minorities, it has never thrown out a map for partisan gerrymandering. Some justices in the past have said the courts have no role in the process; it is between voters and their representatives.

In Monday’s cases, the court said in an unsigned opinion that the status of the Maryland challenge — there has been no trial in the case — counseled against a definitive ruling. They returned the case to a lower court for more work.

And Chief Justice John G. Roberts Jr. said that the plaintiffs in Wisconsin had not shown they were hurt individually by the legislature’s actions, a necessary component for courts to intervene.

“The opinion of the court rests on the understanding that we lack jurisdiction to decide this case, much less to draw speculative and advisory conclusions regarding others,” Roberts wrote for a unanimous court. He said, however, that the Wisconsin plaintiffs should have another chance to show a lower court that they had been individually harmed by the legislature’s actions.

Justice Elena Kagan wrote a concurring opinion, joined by the court’s other liberals, that provided a glimpse of what might have been.

She said courts must find their footing to stop a partisan process that is “degrading the nation’s democracy,” and that map-drawing software only makes it easier to draw precise lines.

Partisan gerrymanders have “become ever more extreme and durable, insulating officeholders against all but the most titanic shifts in the political tides,” she wrote. “The 2010 redistricting cycle produced some of the worst partisan gerrymanders on record. The technology will only get better, so the 2020 cycle will only get worse.”

Kagan laid out a road map for future challenges, including under a test Kennedy has proposed: that partisan redistricting schemes might be judged as punishment for voters because of their past political allegiances, which would violate the First Amendment.

Pending before the court is a challenge of North Carolina’s redistricting. In the battleground state, line-drawing by the Republican-led legislature in 2011 led to the GOP capturing 10 of 13 congressional districts. A state legislator is on record as saying that is only because map-drawers could not figure out a way to give Republicans the advantage in 11 districts.

The Wisconsin case, Gill v. Whitford, was also an extreme one. A panel of three federal judges ruled 2 to 1 that the state’s leaders went too far in using a secretive process for drawing the maps after the 2010 Census.

The lower court concluded that the districting plans were drawn to eliminate swing districts and create ones favorable to Republicans. That court found that the shape of the districts could not be explained by nonpartisan reasons and that the advantage given to Republicans would be “enduring” through the decade even if Democrats outperformed Republicans at the polls.

The judges said Republicans crammed Democrats into some districts and spread them out thinly across others as a way to create more districts conducive to a GOP candidate. The process is called “packing” and “cracking.”

The plans, developed in 2011 by Republican leaders who controlled the legislature and signed by Gov. Scott Walker (R), were effective.

In the election held after the new district maps were adopted, Republican candidates won 48.6 percent of the statewide vote but captured a 60-to-39 seat advantage in the State Assembly.

But Roberts said such statewide evaluations were not the way to go. “To the extent the plaintiffs’ alleged harm is the dilution of their votes, that injury is district specific,” Roberts wrote.

He said the court has similarly decided that “a plaintiff who alleges that he is the object of a racial gerrymander — a drawing of district lines on the basis of race — has standing to assert only that his own district has been so gerrymandered.”

Paul Smith, a Washington lawyer who represented the Wisconsin challengers, said they would accept the court’s invitation to return to lower court with plaintiffs spread across Wisconsin. He said the ruling provides his side with a “great deal of options . . . and running room.”

At oral argument, Roberts had criticized a test the challengers proposed for deciding when districts had been unfairly gerrymandered as “sociological gobbledygook.”

Monday, he was more restrained, saying the problem with the test is that it measures the effect a gerrymander has on the fortunes of political parties, not individual voters.

The difficulty with the Maryland case, the court said in the unsigned opinion, is that it concerned a request from challengers that courts step in now to keep 2018 elections from being held in districts that have been in place since 2011.

There was no reason to do that before a trial has taken place in Benisek v. Lamone, the ruling said.

Maryland Democratic leaders set out in 2011 to redraw the state’s congressional districts to boost the likelihood that the party’s 6-to-2 edge in the delegation became 7 to 1.

Former governor Martin O’Malley (D) was frank about the effort in a deposition in the case, saying partisan advantage was “clearly my intent.”

O’Malley now says he believes redistricting should be done by an independent commission rather than by legislators.

The Democratic mapmakers had to make only minor changes to one district to adjust for population shifts documented in the 2010 Census.

Instead, they moved hundreds of thousands of voters out of the district, and approximately the same number back in, but in a way that gave Democrats an advantage.

The incumbent in the district, longtime Rep. Roscoe G. Bartlett (R), had been reelected in 2010 by a 28-percentage-point margin. But he lost to a Democrat in the redrawn district in 2012 by 21 points.

Attorney Michael Kimberly, representing the Maryland challengers, said he hoped the lower court would order a trial quickly. If successful, he said, that would mean the 2020 elections could take place under a different map.