With confirmation hearings for Judge Brett Kava­naugh nearing, we should look more closely at why Justice Anthony Kennedy’s retirement and Judge Kava­naugh’s nomination have provoked such intense concern and even anger among liberals and progressives. The heated reaction is a matter of simple arithmetic: The one-vote switch from a centrist like Kennedy to a judicial conservative jeopardizes the prospects for liberal/progressive constitutional claims.

But why is that single vote so important? It is because of a huge—and relatively recent—change in the Court’s functioning: the justices’ sharply increased willingness to decide contested issues of constitutional law by a narrow 5-4 majority. This practice, nowadays considered normal and acceptable, was almost entirely unknown from the Court’s earliest days until well into the 20th century. For most of its history the Court operated under an institutional norm that prized consensus and sought to achieve unanimity or near unanimity. The demise of this culture, and its replacement by one that tolerates knife-edge constitutional rulings, happened within living memory.

Until the early 1940s, the percentage of unanimous cases was in most years at least 80 percent, and splits of 5-4 or 4-3 were exceedingly rare. Since then, the overall percentage of 5-4 decisions has risen to 16.6 percent; before then it exceeded 5 percent only 10 times in 140 years. No one knows for sure why this change happened.

Yet this change alone wasn’t sufficient to raise the stakes on Supreme Court nominations as high as they have become, and they did not immediately become the donnybrooks we’re now familiar with. It wasn’t until the 1970s that the Court’s culture normalized the combination of narrow decisions and a freewheeling willingness to make controversial constitutional rulings. A study by Fordham Law professor Jed Shugerman shows that this culture took root in the 1970s when, although the chief justice was the conservative Warren Burger, the intellectual leadership of the Court rested with the very liberal Justice William Brennan and his allies. As Shugerman puts it, “Perhaps more than any other bloc of five, the Burger Court liberals are responsible for the decline of consensus that led to the current problem.”

Justice Brennan was unapologetic and even triumphalist about exploiting a narrow majority to achieve his ideological ends. Harvard Law professor Mark Tushnet recounts this anecdote in A Court Divided: “Each year Brennan asked his law clerks to name the most important rule in constitutional law. Brennan gave them the answer after they stumbled around, naming one great case after another. ‘This,’ he said, holding up one hand with his fingers spread, ‘is the most important rule in constitutional law.’ Brennan knew that it took five votes to do anything, and, he may have thought, with five votes you can do anything.”

That culture having been normalized in the 1970s by what Shugerman calls “the bloc of five liberals,” conservatives promptly made it their own. After being de-Brennanized, the Court, now led by conservative Chief Justice William Rehnquist, declared unconstitutional no fewer than 15 federal statutes by 5-4 votes.

The new culture has survived even a pointed critique by Chief Justice John Roberts, who, upon taking office, announced publicly that he hoped to restore the norm of consensus, warning that if the Court did not “refocus on functioning as an institution, . . . it’s going to lose its credibility.” But even a chief justice so committed—and holding office when Gallup polling shows a near historic low in confidence in the Supreme Court—has been unable to uproot the culture of rendering narrow decisions on highly contested constitutional issues. And it is because of that culture that the Kava­naugh confirmation hearings are likely to be so fiery.

Is there a way to undo the one-vote norm? It seems most unlikely that the Court will itself return to consensus. To take just a few recent examples, 5-4 decisions blocked a full recount in the 2000 presidential election, legitimated the Affordable Care Act, struck down campaign spending limitations, sustained the “essential holding” of Roe v. Wade, and declared gay marriage a constitutional right. Justice Antonin Scalia assuredly spoke for more than just himself when, at a law school conference, he responded with a sarcastic “Good luck” to a question about Roberts’s wish for consensus decision-making.

Another theoretical possibility would involve Congress’s imposing by statute a requirement that a “supermajority” of at least six justices would be needed to declare a law unconstitutional. The supermajority idea has deep roots in American history: Over 60 such proposals—sometimes requiring six votes, sometimes seven, sometimes unanimity—have been made, including by senatorial progressives in the 1920s.

But the salient fact is that none of these proposals was enacted, and apparently only one even received a congressional vote. Congress has demonstrated extreme skittishness about steps that might appear to impinge on the independence of the federal judiciary. Beyond this, there is good reason to doubt that Judge Kava­naugh’s opponents would be willing to live with a supermajority rule, since the wheel turns, and Supreme Court appointments will one day be in their hands again. Further, each side of the divide would harbor suspicions that after accepting a super­majority for “its” Court, the standard would be repealed by the other side once it took power.

The confirmation process itself could be used to challenge the culture of sharply divided constitutional rulings. While Judge Kava­naugh should not be asked—or, at least, should not answer—questions about how he would rule on particular issues, there is no reason he can’t be asked whether he thinks the Court should at least try to function more often by consensus or if he is satisfied that a bare majority is all that should be needed to constitutionally invalidate a law. But neither side is likely to introduce that subject into the confirmation process, lest it come back to bite them in the future.

Lost in the political divide is the important policy question of whether it is truly appropriate for sharply divided decisions to determine our constitutional law—which, it bears emphasizing, means imposing permanent nationwide rules and precluding public decision-making by the ordinary legislative process. Some students of the problem seem unperturbed by that now-routine practice. Harvard Law’s Cass Sunstein concludes his study of the issue with this confident assertion: “The post-1941 norm cannot be shown to compromise the Court’s role in American government, or to disserve the constitutional order.”

But one may well ask why five justices should have the power to lay down a body of law that is beyond democratic reach if they cannot persuade even one of their dissenting fellow justices that the Constitution compels that result. One may marvel that the transformation of the Court from an institution governed by a norm of consensus to one ruled by momentary majorities happened without public debate or awareness. One may even speculate that the Court’s evolution into a nonconsensual institution is one of the wellsprings of the sharp cultural divide in the country itself, and that an institution whose function is to settle great questions on a broadly acceptable basis has somehow, under our very eyes, morphed into one that does exactly the reverse.

If the heat that attends the Kava­naugh nomination provokes careful thought about these questions, it will have served the country well.