By Cokie Roberts and Steven V. Roberts

Just about everybody in Washington can agree on at least one thing: Partisan rancor is rising, while decency and civility in public life are declining. One key reason for that deeply damaging trend: Congressional districts are increasingly drawn to create safe seats for one party or the other.

As a result, lawmakers have a diminishing incentive to listen to their opponents or cooperate across party lines. Representatives pride themselves on being “the People’s House,” but in fact, they have insulated themselves from accountability. They generally fear only a primary challenger from the extreme right or left. The Georgia district that Republicans retained in a hotly contested special election was engineered to protect the GOP and has been easily defended by the party for close to 40 years.

Now the Supreme Court actually has a chance to do something about this poisonous problem. It has accepted a case from Wisconsin that poses a basic question: Is there a constitutional limit to majority rule? Is there a point at which legitimate political interest becomes an unlawful misuse of power?

The courts have been clear: Using political advantage to discriminate against racial minorities is impermissible. But repressing partisan rivals is a very different legal issue.

“The justices have never been able to identify the specific point at which states cross the constitutional line,” Texas law professor Steve Vladeck told CNN. “In this case, a lower court held that Wisconsin had indeed crossed that line. If the justices agree, it would be the first time the court has articulated a constitutional rule in this context, which could — and likely would — have enormous ramifications nationwide.”

Changing how congressional districts are drawn is no cure-all. Hyper-partisanship is caused by many factors: media echo chambers that reinforce existing prejudices and quash dissenting voices; well-heeled interest groups that demand purity on their pet issues; voters who sort themselves into like-minded communities.

Moreover, give credit to Republicans, who have shrewdly invested enormous resources in seizing control of state legislatures and governorships. The GOP went from controlling 36 legislative chambers before the 2010 census to 60, and that enabled the party to dictate the electoral maps in many states. In Pennsylvania in 2012, for example, voters cast 83,000 more votes for Democratic congressional candidates, yet Republicans dominated the state delegation 13 to 5.

To be sure, Democrats adopted equally distorted maps in the few states, like Maryland, where they enjoyed their own leverage. But their record of retribution doesn’t compare to the GOP.

In the Wisconsin case the court has accepted, Republicans won only 48.9 percent of the statewide vote, but captured a 60-39 seat advantage in the State Assembly. Sure, some of that margin stems from the fact that many Democratic voters crowd into cities like Madison and Milwaukee and are therefore “wasted.”

But as Circuit Court Judge Kenneth Ripple, a Ronald Reagan appointee, concluded: “We find that the discriminatory effect is not explained by the geography of Wisconsin, nor is it justified by a legitimate state interest. Consequently (the political map) constitutes an unconstitutional political gerrymander.”

Gerrymanders are hardly new. The phrase was coined after Massachusetts Gov. Elbridge Gerry signed a law in 1812 creating a voting district shaped like a salamander. But sophisticated computers, in the hands of highly partisan map makers, have made the problem much worse.

Presumably that’s why the high court agreed to take this case. When the justices last visited the issue in 2004, in a suit called Vieth v. Jubelirer, four liberal justices agreed there is such a thing as an “unconstitutional political gerrymander.” Four conservative justices said the court should not get enmeshed in such political matters.

The swing vote, Justice Anthony Kennedy, sided with the conservatives but wrote an important concurring opinion. He presciently predicted that “computer-assisted districting” would aggravate the problem in the future, and “the temptation to use partisan favoritism in districting in an unconstitutional manner will grow.”

If that temptation was “applied in an invidious manner,” Kennedy wrote, and if judges could establish a “manageable standard” for evaluating that malice, then a later court might well put limits on unbridled political power grabs.

That time has come. The future that Kennedy foresaw 13 years ago has arrived. If he is true to his own words and values, he will vote with the court’s four liberal justices and state clearly that political power is not unlimited.

Winning an election is not a license to abuse that power.

The health of American democracy could well depend on his judgment.

Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.