– The Supreme Court was told Tuesday that it is the "only institution in the United States" that can prevent a coming wave of extreme partisan gerrymandering that would distort the basic structure of democracy.

But the justices seemed split about whether they could find a "manageable" way of determining when politics plays too big a role in drawing legislative districts that are the building blocks of representative government.

The deciding vote will likely be cast by Justice Anthony Kennedy, and lawyers for challengers of the plan had to be happy with what they heard from him at the hourlong oral argument.

He gave a hard time to those defending Wisconsin's 2011 redistricting plan, which has been criticized as one of the most extreme versions of partisan gerrymandering in the country. He asked no questions of the challengers' lawyers.

He pressed the state's lawyers about whether it would be unconstitutional for the state to simply declare that it was going to favor one party over another. They reluctantly answered that it would, but denied this challenge fit that framework.

Washington lawyer Paul Smith, representing challengers, told the justices that if they let Wisconsin's redistricting plan stand, the court would create "a festival of copycat gerrymandering the likes of which this country's never seen." States are required to draw new legislative and congressional districts after each decade's census.

But Chief Justice John ­Roberts pushed back. He said Smith was asking the courts to effectively take over the process of redistricting from elected officials, something he said would lead the public to question the "status and integrity of decisions of this court."

If the court opens the door to partisan challenges, he said, "every one of these cases will come here. We will have to decide in every case whether the Democrats win or the Republicans win."

The court may rely on mathematical theories and scientific predictions on what makes a plan too partisan, Roberts said, but a member of the public will say "baloney."

Other conservative justices who asked questions had similar worries about exactly how the court could make such evaluations. Wisconsin Solicitor General Misha Tseytlin said the challengers had brought nothing new to help the justices since the last time the court decided not to invalidate a state's plan, in 2004.

Liberal justices seem to think the court needs to be involved in partisan gerrymandering, just as it evaluates plans for racial gerrymandering. Justice Ruth Bader Ginsburg said what was at stake was "the precious right to vote."

With partisan gerrymandering, "the result is preordained" in many districts.

When lawyers for the state said any evaluation of a plan would necessitate the court to rely on predictions of voter behavior, Justice Elena Kagan said that would not be hard.

"The world of voter technology has changed a great deal," she said. Just as lawmakers use the technology to design districts most favorable to the political party involved, so, too, can challengers, and courts, use it to discover when it is entrenching that party in power.

Justice Stephen Breyer proposed a test to include whether one party was in control of the process, whether each party would have a chance to control the legislative body if it got similar amounts of votes, whether there was a persistent unfairness, whether the map was an "extreme outlier" from other states and whether there was any neutral justification for the way the challenged map was drawn.

It is similar to how a lower court decided Wisconsin's map was unconstitutional.

The justices have never thrown out a state's maps because of partisan gerrymandering. But challengers from Wisconsin say they have the evidence that Republican leaders of their state drew maps to ensure enduring GOP control of the legislature, and a test for deciding when political advantage goes too far.

The outcome could change the way U.S. elections are conducted. Wisconsin officials say if their maps, which follow traditional redistricting standards, are illegal, dozens of state plans will need to be thrown out.

Waiting in the wings are gerrymandering complaints from North Carolina and Maryland. The Maryland case alleges that the state's Democratic leadership drew congressional maps that put the GOP at a disadvantage.

The court routinely makes states redraw maps when there is evidence that drawing of legislative maps harms minority voters by making it more difficult to elect representatives of their choice.

Individual justices have said partisan gerrymandering is harmful as well. But even some of those who agree have said redistricting is a political question between representatives and their constituents, and the courts should stay out.

Others — most importantly, Kennedy — have said extreme partisan gerrymandering can violate constitutional rights. But in the court's most recent look at the issue in 2004, he did not find a workable test for deciding what is excessive.

In the Wisconsin case, a panel of three federal judges ruled 2 to 1 that the state's leaders had used a secretive process for drawing the maps after the 2010 census that went too far.