Protesters opposing gerrymandering outside the U.S. Supreme Court. (Sarah L. Voisin/The Washington Post)

Opponents of gerrymandering — i.e., Democrats — just secured an important victory in a federal appeals court, when a three-judge panel ruled that Ohio’s congressional maps are an unconstitutional partisan gerrymander.

“We are convinced by the evidence that this partisan gerrymander was intentional and effective and that no legitimate justification accounts for its extremity,” the judges wrote. “The 2012 map dilutes the votes of Democratic voters by packing and cracking them into districts that are so skewed toward one party that the electoral outcome is predetermined.”

“Packing and cracking" describes taking the other party’s voters and packing them into as few districts as possible, so they win overwhelming victories, or cracking them into minorities in districts where the party is then guaranteed to lose. These tactics are how map-drawers “waste” the opposition’s voters, rigging statewide balances of power.

The Republicans who gerrymandered in Ohio after the 2010 Census were very successful. This swing state’s congressional delegation includes 12 Republicans and just four Democrats. In the 2018 elections, the Republican candidates got 52 percent of the statewide two-party vote for House and the Democrats got 48 percent, but Republicans held 75 percent of the seats.

This map will now have to be redrawn. But the big question now is how long this victory will last.

The Supreme Court has never ruled partisan gerrrymandering unconstitutional. But in March the high court heard a case involving the gerrymanders in North Carolina (made by Republicans) and Maryland (made by Democrats). We’re still awaiting the court’s decision in that case.

But it doesn’t look promising. Judging by oral arguments in that case -- and in another recent gerrymandering punt by the court -- the conservative justices seem to believe there’s no workable standard to distinguish between a map gerrymandered so unfairly that it violates the Constitution, and one that doesn’t, even if they wanted to.

In the Ohio ruling, judges ruled that an overly partisan gerrymander is created when the outcome of elections is “predetermined” to a degree that unconstitutionally violates voters’ right to political association by making it harder for some voters to advance their political aims.

But this decision will ultimately be appealed to the Supreme Court -- and with the other cases also being heard, there’s little reason to think this will be upheld.

Recent events have created a bleak outlook. Senate Majority Leader Mitch McConnell (R-Ky.) refused to give Merrick Garland a hearing, resulting in Antonin Scalia’s seat being filled with Trump nominee Neil M. Gorsuch. Then came the retirement of Anthony M. Kennedy -- the one conservative who has seemed open to finding some kind of standard for declaring gerrymanders unconstitutional. Once President Trump filled Kennedy’s seat with Brett M. Kavanaugh, that meant five conservative justices who appear hostile to policing partisan gerrymandering.

But it actually could get worse than this.

Multiple states have responded to gerrymandering on their own, by putting in place -- either through legislation or popular referendum -- some form of redistricting commission that dilutes the direct power of politicians over district lines. Several states just installed such commissions in the 2018 elections.

Ohio voters also passed such a measure, approving by a 75-to-25 percent margin an initiative requiring what is essentially bipartisan agreement in the legislature on a new map to be drawn after each census (it won’t take effect until after the 2020 election). Such solutions, then, are popular -- and gerrymandering is not.

But as election scholar Rick Hasen has noted, it’s not clear how long those commissions will be allowed to stand.

The problem resides in a 2015 case. Four conservative justices argued that any redistricting commission created by the voters in an initiative is unconstitutional, and the power should lie solely with the state legislature. That failed -- because Kennedy sided against the conservatives. But now, if another such case comes up, with Kavanaugh (and Gorsuch) on the court, five conservative justices could nullify some or all types of commissions.

The result would be that the Supreme Court won’t police partisan gerrymanders -- and won’t allow states to address the problem themselves. That would be a huge boon to Republicans -- yes, Democrats have a long history of these tactics, but in recent years, the primary offenders have been Republicans -- in many states across the country.

For the full story on all of this, check out Greg’s new book, which also recounts the ugly history of how we got to this moment.

By the way, since we’re talking about counter-majoritarianism and the Supreme Court, you should know that there are now four justices who were confirmed by senators representing a minority of national voters, and if Trump fills another seat, a majority of the court will likely have been confirmed in this manner. And all five will also have been chosen by presidents who initially ascended to the White House after losing the popular vote.

This is a good day for fair elections. But the victory may be only temporary. And the counter-majoritarianism is likely to get worse.

Read more:

George F. Will: The Supreme Court should steer clear of gerrymandering cases

Roy Cooper and Larry Hogan: Take it from us governors: Politicians shouldn’t draw electoral maps

Henry Olsen: Courts can’t solve our gerrymandering problem. Take it from a former gerrymanderer.

The Post’s View: Missouri Republicans want to undo voters’ redistricting wishes. The Supreme Court should take note.

Steve Neal: We can fix gerrymandering. It’s a matter of choosing the right words.