With the prospect before us that on Saturday Donald Trump—a president loathed without limit by liberals—will nominate a conservative to the Supreme Court in the shadow of the 2020 election, we’d say “The Godfather” offers a more apt description of our politics just now: We are “going to the mattresses.” To quote Consigliere Chuck Schumer: “Nothing is off the table.” Nancy Pelosi is threatening fusillades of arrows.

How American politics went from live-and-let-live to tribal war is a long story, but the issue in front of us now is the Supreme Court of the United States.

That subject alone surfaces an important right-left distinction. While conservatives typically talk about “the court” as an institution and its competing judicial philosophies, Democrats and the left prefer discussing the court in terms of discrete policy goals, such as abortion or various public services.

Thus did Democratic Sen. Dianne Feinstein summarize the battle this week: “Let’s be clear what’s at stake—health insurance for millions of Americans and lifesaving protections for the 129 million people with pre-existing conditions.” It’s about more than that.

In conservative circles, a famous date in the political system’s descent into total war is 1987 and the hearings into Reagan’s nomination of Robert Bork to the Supreme Court. Those hearings—actually, a show trial—were presided over by Judiciary Committee Chairman Joe Biden, an exercise that included the public excavation of Judge Bork’s history of video rentals, which ironically included Alfred Hitchcock’s “The Man Who Knew Too Much.”

With respect, we would like to call Robert Bork back as a witness to what happened to American politics and why we are going to war over what looks to be the nomination of the first conservative woman to the Supreme Court, likely either Judge Amy Coney Barrett or Judge Barbara Lagoa. Back in 1971, Bob Bork saw what was coming.

In an unstated homage to prescient Lewis Carroll’s Queen of Hearts (“Sentence first, verdict afterwards!”) Bork called judging based on personally derived values, “Decisions first, principles later.”

But Bork didn’t find much to be amused about in where such judging would take American democracy, which he posed as a question. What does a man conclude, he asked, about “a Court that does not share his politics or his morality? I can think of nothing except the assertion that he will ignore the Court whenever he can get away with it and overthrow it if he can.”

And here we are, with prominent Democrats such as Rep. Jerrold Nadler and Sen. Edward Markey and liberal commentators promising to pack the court with additional justices if President Trump (whose 2016 election Democrats have rejected daily the past four years) doesn’t stand down from his constitutional right to appoint RBG’s replacement. They will overthrow the current court, if they can.

A main element of the election is tension between the Biden-led Democratic establishment and the ascendant Sanders-Warren progressives. As Rep. Alexandria Ocasio-Cortez acidly put it: “Voting for Joe Biden, it’s not about whether you like him or not, it’s a vote to let democracy live another day.”

Mr. Biden didn’t create this division during the primaries. The Democratic Party has been moving leftward for years on policies affecting personal rights claims, the environment and regulatory authority—so much so that the possibility of liberal-conservative legislative compromise in Congress all but disappeared.

Ever resourceful, the left turned to filing policy-outcome lawsuits whose goals were implemented by policy-oriented federal judges, effectively making the courts a parallel legislature. Decisions first, principles never.

The culture wars fought in so many presidential elections didn’t originate in legislatures. They came out of left-liberal judicial decisions. A Barrett or Lagoa Supreme Court won’t “make” conservative policy. It likely will force policy making back into legislatures, where it belongs.

Robert Bork asked 50 years ago whether Americans understood enough of what was happening to the courts to be able to say they had consented to it. The left’s use of the judiciary as a parallel legislature has rarely been put clearly before Americans, in large part because Democratic candidates won’t talk about it.

With this nomination, which the Senate may confirm days before the election (the real one Nov. 3, not the mail-in tabulation weeks later), Mr. Trump is forcing an important and overdue choice before the country’s voters. We’ll see in Tuesday’s debate whether Mr. Biden can get through the evening ducking the question of the court’s proper role.