If you can’t win, change the rules. That’s the Democratic Party’s new playbook. Democrats are urging the US Supreme Court to redraw Wisconsin’s electoral map, claiming Republican lawmakers drew it unfairly.

If the justices toss Wisconsin’s map and dictate new rules for election mapmaking, it could turn winners into losers and vice versa in many states. Republicans have been on a winning streak and now control both legislative houses in 33 states, including Wisconsin. They rightly oppose this judicial interference. The justices will hear the case, Gill v. Whitford, on Oct. 3.

Democrats claim Wisconsin’s election map puts them at a disadvantage by packing their voters into too few election districts, “wasting” their votes and allowing Republicans to win the majority of districts.

But the real problem isn’t an unfair map. It’s that Wisconsin Democrats are concentrated in cities. In many states, Democrats tend to win urban voters and do less well with suburban and rural voters. Wisconsin Democrats want the lines redrawn so their urban voters can capture a majority of the state’s legislative seats — and they’re asking the Supreme Court to help them.

It’s a brazen political gambit disguised as fairness. They claim to be victims of gerrymandering — drawing election districts to favor one party. But they’re not opposed to gerrymandering. They just want it to favor them.

They hope a Supreme Court victory will restore their political fortunes after the 2020 Census, when states have to redraw their electoral maps.

If Democrats prevail in court, the nation’s political map could change significantly after the Census, with many statehouses flipped to Democratic control. That would likely mean higher state taxes, anti-fracking laws and job-killing regulations on business.

As for gerrymandering, it’s been around for over 200 years and isn’t limited to any party.

When James Madison ran for Congress in 1788, rival politicians, including his mortal enemy Patrick Henry, drew district lines to try to exclude Madison’s supporters. Madison won anyway, but manipulating voting districts for partisan advantage was just getting started.

Massachusetts Gov. Elbridge Gerry, a signer of the Declaration of Independence and Constitutional Convention delegate, raised it to an art form in 1812, carving a bizarre district in his state that meandered around Boston like a salamander. A Boston newspaper caricatured it, adding claws, fangs and a tail, and called it a Gerry-mander.

That political monster has been with us ever since. It’s one of the tools pols in both parties use — along with arcane ballot-access rules and the perks of incumbency — to rig elections and exclude competition.

At its worst, it deprives voters of any meaningful self-government. But this corrupt gerrymandering should be cleaned up by the voters — not the federal courts.

Is there a practical solution? Yes. Voters in 13 states have already set up independent or bipartisan commissions to draw district lines after each Census.

In 2014, New York state approved a constitutional amendment establishing a redistricting commission, but unfortunately it allows the Legislature to ultimately reject whatever map the commission proposes. Iowa’s remedy is better, barring any consideration of partisan affiliation when lines are drawn.

But don’t confuse that with what Wisconsin Democrats are trying to do. In Wisconsin, there are no salamander-shaped election districts. But Democrats want to rig the rules to increase the clout of urban voters, even if it requires drawing strangely shaped districts.

In the past the Supreme Court has refused to meddle in partisan gerrymandering cases. As Justice Antonin Scalia explained in a 2004 ruling, “political gerrymandering claims are nonjusticiable” — meaning strictly political matters. That’s how the justices should rule again in the Wisconsin case. If Democrats want to return to power, they’ll need to broaden their appeal and win over more of America’s nonurban voters.

Betsy McCaughey is a senior fellow at the London Center for Policy Research.