Going into the oral arguments for Moore v Harper on Wednesday, it was easy to forget just how radical and strange it was that the US supreme court was hearing the case in the first place.

Moore v Harper is a challenge by North Carolina’s Republican-controlled state legislature to a decision by the state’s Democratic-controlled supreme court, which threw out what the court called an excessively gerrymandered congressional district map that the legislature put forward, saying the map violated a state constitutional law guaranteeing free elections. Unhappy, the legislature adopted what used to be a fringe theory: that state courts don’t have much jurisdiction over election matters at all.

This used to be the kind of claim that a different supreme court would never dignify by granting certiorari. The “independent state legislature” theory has been put forward only a handful of times over the past hundred years, and even then, only by blatant partisans acting in transparent bad faith.

But “blatant partisans acting in transparent bad faith” is now a decent description of the supreme court, so the meritless case is being heard this term. And the North Carolina legislature’s gambit even has a shot of succeeding. When oral arguments began on Wednesday morning, the theory advanced by the legislature had garnered public expressions of support by four of the nine sitting justices – Samuel Alito, Neil Gorsuch, Brett Kavanaugh and Clarence Thomas. As happens so frequently with this court, a theory that was once confined to the radical rightwing fringe has been ushered into doctrinal legitimacy by judges eager to secure conservative outcomes.

The independent state legislature theory posits that, when it comes to determining how to conduct federal elections, state legislatures have virtually no limits on their authority and no other government bodies that can check them. State constitutions can’t limit how legislatures order elections, according to this theory, and neither can state courts.

It’s an odd conception of state legislatures, picturing their power over elections as special and different, not subject to the ordinary checks and balances of executive actions and judicial review. Under it, all state constitutional provisions that protect voting rights, ensure equal protection of the law and guarantee due process would be moot, as far as elections go; legislatures would not be bound by them.

And it’s a vision of state legislative authority in elections that the supreme court has rejected as recently as 2015: in Arizona State Legislature v Arizona Independent Redistricting Commission, the court ruled that voters could use a ballot initiative to create an independent commission to draw new congressional districts. The North Carolina legislature, meanwhile, has itself asked the state supreme court to weigh in on certain election administration questions, making their own claim that that court has no authority on such issues seem odd. If it were adopted by the federal supreme court, the independent state legislature theory would call a mulligan on all of this, disposing of the regular relationship between state legislatures and state courts along with about 100 years’ worth of precedent.

Applied to appointing electors every four years for the presidential election, this was the theory that backed the election subversion plot cooked up by Trump adviser and disgraced law professor John Eastman: it was the theory that if a state legislature didn’t like the electors dictated to them by the voters of their states, they could simply advance another slate of electors instead.

The case before the supreme court now applies the theory to federal congressional elections. It posits that if a state legislature wants to draw a dramatically gerrymandered congressional map – the kind that dilutes the value of votes, erodes the competitiveness of elections and forecloses the ability of the people to express their will through the political process – then it can. State legislators have to abide by the rule of law, according to the theory – except for when they’re determining the rules by which they get to remain in power.

Moore v Harper has come to be seen as an existential threat to functioning democracy in America, in no small part because, in the hands of insurrectionists like Eastman, the tenets of the independent state legislature theory have already become fodder for an attempted coup. But it seems that what might decide the fate of the theory is not its threat to the integrity of implementation but practical matters of applicability.

At oral arguments on Wednesday, the liberal justices hammered lawyers for North Carolina’s legislature about the unaccountable extra-constitutionality of the scheme. Even the arch-conservative Samuel Alito seemed less than enthused, though there’s no doubt he will support the theory when it’s time to issue opinions. But as in most cases this court hears, those votes were never really in play: Alito will vote for whatever seems favorable to the Republican party; Gorsuch seemed downright excited about the theory at oral arguments; and Thomas’s wife, Ginni Thomas, lobbied for the theory in the aftermath of the 2020 election.

Meanwhile, Chief Justice Roberts has been publicly skeptical of the theory, and didn’t give much indication at oral argument that he had changed his mind. Brett Kavanaugh, ever eager to grasp at some semblance of moderation and respectability that might make the public forget that there are multiple credible accusations of sexual assault against him, seems eager to split the baby; he’s indicated in the past that he would prefer a smaller nullification of state judicial review than what the North Carolina legislature is asking for. Theirs are not the votes that matter, in the end. The vote that matters is Amy Coney Barrett’s.

And so it was exceptionally good news for the country that the Trump appointee appeared skeptical of the petitioner’s argument on Wednesday. The theory, it was pointed out, would create chaos in the federal courts, delegating huge numbers of murky elections disputes to the federal judiciary as state courts are stripped of jurisdiction. The North Carolina legislature’s attorneys tried to make an obscure distinction between “substantive” elections questions, which state courts would not be able to rule on, and “procedural” questions, which they would; Barrett wasn’t buying it, correctly pointing out that that very distinction was likely to be disputed.

The theory would create different rules for state and federal elections, fomenting chaos that would enable those with the worst motives to serve their own interests, instead of the country’s. Hopefully, that prospect won’t appeal to Barrett. But the chaos was always precisely the point.

• Moira Donegan is a Guardian US columnist