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WASHINGTON — A majority on the U.S. Supreme Court suggested Wednesday that Maryland took partisanship too far when it changed the boundaries of a congressional district to help Democrats. But the justices struggled with what to do about it.

Republican voters are challenging the redrawing of Maryland's 6th Congressional District in 2011, which gave Democrats a seat in the U.S. House of Representatives that a Republican held for two decades.

But because partisanship is always a factor when political boundaries are redrawn by the party in the majority, a central issue in this case is how to know when it goes too far.

"However much you think is too much, this case is too much," said Justice Elena Kagan. "How much more evidence of partisan intent could we need?"

A Republican, Roscoe Bartlett, held the seat for 20 years and won by a 28 percent margin in 2010. After the redistricting, he lost by a 21 percent margin.

Michael Kimberly, a lawyer representing the Republican challengers, told the court that the blatantly partisan gerrymandering violated the First Amendment.

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The new 6th District boundaries, he said, retaliated against Republicans who had supported Bartlett in past elections. "Government officials cannot single out citizens based on their political views."

But the court appeared concerned that a ruling for the Republicans in this case, with obviously partisan intent, would open the door to challenges when political considerations were not as blatant.

"The problem," said Justice Stephen Breyer, "is that we will never have such a clear record again. So what are we to do?" He asked if there could be a "practical test that won't get judges involved in every redistricting."

The First Amendment test advanced by the Republican challengers in Maryland seemed too vague for Justice Samuel Alito, who asked, "How could any legislature ever be able to redistrict, if it picks a plan that favors any party?"

Steven Sullivan, Maryland's solicitor general, said the state did not simply consider partisan advantage in drawing the new 6th District boundaries.

Among other factors, he said, was eliminating a crossing of the Chesapeake Bay.

The court pondered a similar question last fall when it heard a partisan gerrymandering case from Wisconsin involving new boundaries for the entire state's legislative districts.

Rep. Roscoe Bartlett, R-Md., right, campaigns for his seat in 2012. Bill O'Leary / The Washington Post/Getty Images file

Based on the questions and comments from the justices during Wednesday's argument, the court apparently has not come up with a satisfactory resolution of that case, either. Though it was argued in October, the court was likely holding it until it heard the Maryland case.

At one point on Wednesday, Justice Breyer suggested that the court could combine the Wisconsin and Maryland cases with another from North Carolina and take up the issue next year, with lawyers for each side allowed to advance and criticize possible ways to develop a test for excessive partisanship.

It's unlikely Breyer would have offered such a suggestion if the court had already come up with a satisfactory way to decide the Wisconsin case.

Until recently, federal courts rejected claims of excess partisanship in gerrymandering, concluding that such disputes were inherently political, not legal.

But last year, a panel of three federal judges struck down state house district maps drawn in 2011 by Wisconsin's Republican controlled legislature, finding the results were so blatantly partisan that they denied Democrats a fair shot at electing candidates of their choosing. That ruling was the subject of the U.S. Supreme Court's first case this term involving partisan gerrymandering.

And in January, Pennsylvania's supreme court ruled that congressional district boundaries in the state were so obviously drawn to disfavor Democrats that they "clearly, plainly, and palpably" violated the Pennsylvania constitution.