The US supreme court heard arguments on Wednesday in Moore v Harper, one of this term’s highest profile and most contentious cases which has the potential to fundamentally reshape elections for Congress and the presidency.

The justices appeared to be starkly divided along predictable ideological lines as they mulled over the power of state courts to strike down congressional districts drawn by state legislatures because they violate state constitutions.

Republicans from North Carolina who brought the case argue that a provision of the US constitution known as the elections clause gives state lawmakers virtually total control over the “times, places and manner” of congressional elections, including redistricting, and cuts state courts out of the process.

The Republicans are advancing a concept called the “independent state legislature theory”, never before adopted by the supreme court but cited approvingly by four conservative justices.

The direction of questioning at Wednesday’s hearing suggested thatthree of those conservative justices – Samuel Alito, Neil Gorsuch and Clarence Thomas – were open to the idea of adopting the theory, despite decades of precedent from their own court dismissing it. They seemed to have the slightly more tentative backing of Brett Kavanaugh, who was part of the legal team in 2000 that assisted George W Bush through Bush v Gore, the case that in modern times put the independent state legislature theory on the map.

On the other side of the argument, the three liberal-leaning justices were profoundly critical of the notion that state legislatures should be given free rein to control federal elections virtually unrestrained by state constitutions and judicial review from state courts. Questions from John Roberts suggested he might be seeking a more narrowly-drawn compromise position.

Which left all eyes on Amy Coney Barrett, the third of Donald Trump’s three appointees. Potentially, she might find herself casting the decisive vote.

Though it gives little clue as to which side of the fence Barrett will be standing on when the ruling comes down, she did ask several probing questions of the lawyer representing North Carolina’s Republicans. She said that those pushing for state legislatures to be freed up from oversight had a “problem” defining their terms, and she questioned whether the theory had any bearing in legal text.

For their part, the liberal justices – Elena Kagan, Ketanji Brown Jackson and Sonia Sotomayor – robustly argued that incorporating the theory into constitutional law would be a threat to democracy. Elena Kagan cited three recent supreme court rulings that all counter the theory.

Kagan made an impassioned speech about the potential impact of siding with North Carolina’s Republicans. “Think about consequences, because this is a theory with big consequences … This is a proposal that gets rid of the normal checks and balances on the way big governmental decisions are made in this country, at exactly the time when they are needed most.”

She warned that a broad ruling could unleash state legislatures to carry out extreme forms of gerrymandering, tear up voter protections and even certify election results according to their own political interests.

Moore v Harper came about after the North Carolina state supreme court struck down districts drawn by Republicans who control the legislature because they heavily favored Republicans in the highly competitive state. The court-drawn map used in last month’s elections for Congress produced a 7-7 split between Democrats and Republicans.

North Carolina is among six states in recent years in which state courts have ruled that overly partisan redistricting for Congress violated their state constitutions. The others are Florida, Maryland, New York, Ohio and Pennsylvania.

State courts have become the only legal forum for challenging partisan congressional maps since the supreme court ruled in 2019 that those lawsuits cannot be brought in federal court.

In North Carolina, Republican lawmakers will not have to wait for the court’s decision to produce a new congressional map that is expected to have more Republican districts.

Even as Democrats won half the state’s 14 congressional seats, Republicans seized control of the state supreme court. Two newly elected Republican justices give them a 5-2 edge that makes it more likely than not that the court would uphold a map with more Republican districts.

One of the striking features about Wednesday’s legal debate was how the usual ideological positions of the two sides were turned on their heads. The conservative justices, who have often invoked states’ rights in previous rulings – not least in last year’s seminal decision to overturn abortion rights – sounded at times to be almost anti-federalist.

After the US solicitor general, Elizabeth Prelogar, accused the petitioners of making an “atextual, ahistorical, and destabilizing interpretation of the elections clause”, Thomas intervened. “I must say, it seems a bit ironic that you’re on the other side of the federalism issue,” he said, apparently unaware of the irony of his own position.

By contrast, lawyers speaking against the state legislature theory turned on several occasions to the historical record of the founding fathers as well as close textual analysis of the constitution – tactics normally associated with the rightwing supermajority. “Over 233 years, this court has never second-guessed a state court interpretation of its own constitution in any context,” said Neal Katyal, a lawyer representing Common Cause, an ethics-in-government group which is opposing what it claims is an attempted Republican power grab in North Carolina.