WASHINGTON - U.S. Supreme Court justices showed deep divisions Tuesday over a gerrymandering case from Wisconsin that could have far-reaching national implications.

Liberal justices expressed openness to the idea that courts should intervene when lawmakers draw election maps that greatly favor their party. Conservatives were skeptical that judges could come up with a way to determine whether and when legislators had gone too far.

In the middle of it all — as expected — was Justice Anthony Kennedy. Both sides see him as the one who will likely cast the deciding vote and they pitched their arguments to him.

A three-judge panel last year ruled 2-1 that maps for the Wisconsin Assembly were so heavily Republican that they violated the constitutional rights of Democratic voters. Now, the Supreme Court must decide whether the lower court got the ruling right.

Justice Ruth Bader Ginsburg questioned what would happen to the "precious right to vote" with maps like Wisconsin's that lock in a majority for one party.

"If you can stack a legislature in this way, what incentive is there for a voter to exercise his vote?" she asked. "Whether it's a Democratic district or a Republican district, the result — using this map, the result is preordained in most of the districts."

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Chief Justice John Roberts countered that legislatures have long been the ones in most states to determine where political lines are drawn.

“The whole point is you’re taking these issues away from democracy and you're throwing them into the courts," he told the attorney for the group of Wisconsin voters who brought the case.

If they succeed, the nation's high court will have to decide in case after case whether to toss out maps favoring one party over the other, he said. And the public will suspect the court's rulings are based on partisanship, he warned.

“That is going to cause very serious harm to the status and integrity of the decisions of this court in the eyes of the country," he said.

The stakes are high for Wisconsin's Democrats, who have been out of power for seven years. The case represents one of their last shots — if not their very last shot — of gaining a foothold in the Legislature in the foreseeable future.

But the case could also have a broad national impact. If Wisconsin's maps are thrown out, states will have to follow new rules when they draw congressional and legislative districts, limiting their abilities to give edges to either party.

The packed gallery included Arnold Schwarzenegger, the Republican former governor of California who has championed redistricting reform, and Wisconsin Senate Majority Leader Scott Fitzgerald (R-Juneau), one of the top leaders to sign off on the GOP-friendly maps.

The Supreme Court has long wrestled with the question of whether maps can be so one-sided as to violate the Constitution.

Both sides focused their arguments on Kennedy, who has written that overly partisan maps can violate the Constitution but that courts have never had a way to measure when that happens.

He asked Erin Murphy, an attorney for the Wisconsin Legislature, whether it would violate the Constitution for a state to pass a law that required lawmakers to draw maps that gave maximum advantage to one side (while still complying with traditional redistricting principles).

“I’d like the answer to the question," Kennedy said.

Murphy said such a law would violate the Constitution, but emphasized that no such law was in effect in this case.

Wisconsin Solicitor General Misha Tseytlin — a former Kennedy clerk — argued Wisconsin's maps are constitutionally sound and contended a victory by the Democrats would prompt a slew of litigation across the country.

He told the justices the plaintiffs hope to "launch a redistricting revolution" that would force maps around the country to be redrawn.

"I would expect that almost every single map drawn by a legislature will be challenged immediately if plaintiffs prevail," he said by email before Tuesday's arguments.

Those bringing the case disputed that, saying litigation could advance only in states with the most extreme maps.

Paul Smith of the Campaign Legal Center argued the case on behalf of the Democratic voters from Wisconsin. He told the court it was the "only institution" in America that could prevent lawmakers from drawing maps that helped themselves at the expense of voters.

“Politicians are never going to fix gerrymandering," he said. "They like gerrymandering.”

The map for the Wisconsin Assembly, he said, "is so extreme that it effectively nullifies democracy."

The center, based in Washington, D.C., hopes to curb partisan gerrymandering by both sides. Some Republicans — including Schwarzenegger, U.S. Sen. John McCain of Arizona and Ohio Gov. John Kasich — are siding with the Wisconsin Democrats.

”I say it is time to say hasta la vista to gerrymandering and it is time to terminate gerrymandering," Schwarzenegger said on the plaza outside the court.

Every 10 years, states must draw new election maps to account for population shifts. In Wisconsin and most other states, politicians get to draw those lines.

Republicans took full control of Wisconsin's government in the 2010 elections and used their power to draw maps that greatly favor them.

Democratic voters sued in 2015, arguing their voting rights had been violated, and the panel of judges sided with them last year. (Unlike other types of cases, redistricting lawsuits are first heard by a panel of three judges and then go directly to the Supreme Court.)

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The Supreme Court is expected to rule by summer.

Wisconsin is often closely divided, but that doesn't reveal itself in legislative races.

In 2012 — a year when Democratic President Barack Obama handily won Wisconsin — Democrats received nearly 52% of the vote in Assembly races, yet took just 39 of the chamber’s 99 seats.

In last year's election, Republican Donald Trump topped Democrat Hillary Clinton by the slimmest of margins in the presidential race, but the Republicans laid claim to a 64-35 majority in the Assembly.

The Democratic voters who brought the lawsuit contend both sides should have an equal chance to capture the same number of seats. If one side can get 60 seats with 52% of the vote, the other should be able to do the same thing, Smith argued.

They proposed a new test to determine whether maps were unfairly one-sided. It counts “wasted votes” — that is, any votes beyond those needed to elect a candidate — to determine the “efficiency gap” of a map.

Maps have large efficiency gaps when they spread one party’s voters into districts in a way that creates a significant number of wasted votes for them.

Justice Samuel Alito questioned whether courts should adopt a relatively new social science theory rather than waiting for more scholarship. Justice Neil Gorsuch said he was worried new rules would be so vague that states wouldn't know what they were allowed to do.

Roberts called the plaintiffs' test “sociological gobbledygook.”

Justice Stephen Breyer said the social science measurements may be gobbledygook, but the idea of fairness is not and there are efficient ways for courts to determine what's fair.

Justice Elena Kagan said courts should be able to determine if maps are fair by using the same tools lawmakers use to draw maps. Computer programs allow lawmakers to put in place maps they can count on to keep them in power.

“When legislatures think about drawing these maps, they’re not only thinking about the next election, they're thinking often — not always — but often about the election after that and the election after that and the election after that," she said.