Updated June 27, 2023 at 6:42 PM ET

The U.S. Supreme Court on Tuesday repudiated the most extreme form of a controversial legal theory that, if adopted, would have radically reshaped the way elections are conducted, giving state legislatures virtually unchecked power to decide election rules.

By a 6-to-3 vote, the court rejected the so-called Independent State Legislature theory advanced by the Republican-dominated North Carolina state legislature. Writing for the court majority, Chief Justice John Roberts said that the U.S. Constitution does not, as the lawmakers had claimed, insulate their actions from review by the state courts. To the contrary, he said, state legislative power is constrained by the federal and state constitutions, as well as ordinary state laws.

At the same time, however, Roberts said that in overseeing election provisions, state courts "do not have free rein" to exceed "the ordinary bounds of judicial review."

How to know when courts do exceed that power? The court majority didn't say, leaving for another day the task of articulating a standard for determining when federal courts may tell a state court that it has gone too far in interpreting state law.

Joining Roberts in the majority were conservative Justices Brett Kavanaugh and Amy Coney Barrett and the court's three liberals, Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson. Justice Clarence Thomas wrote the dissent, saying first that the case presented no live controversy anymore since a subsequent state supreme court decision had thrown out the original ruling. Justice Samuel Alito joined that part of the dissent only. But Justice Neil Gorsuch joined the second part of the Thomas dissent, which disputed the majority's conclusion on the merits of the case.

Specifically at issue in the case was a decision by the North Carolina Supreme Court holding that the state legislature had violated state constitutional provisions barring partisan gerrymanders. As a result, the state court ultimately drew new congressional district lines for the 2020 election, and the GOP-dominated state legislature appealed to the U.S. Supreme Court. The lawmakers contended that the federal Constitution's provision delegating to state legislatures the power to set the "times, places and manner" of elections means that only the state legislature can make election rules, not courts, and regardless of state constitutional provisions.

Election experts disagreed on the effect of the ruling

NYU law professor Richard Pildes called it "highly significant" that the court rejected the extreme view of the ISL theory. But he said that "at the same time, [the court] endorsed a weaker version of this independent state legislature doctrine, and this is going to sort of hang over the 2024 election."

UCLA law professor Richard Hasen went further, noting that Tuesday's decision gives the federal courts a lot of new power over state courts.

"They've preserved for themselves the right to be the ultimate arbiter of whether state courts have gone too far," he said. The decision "harkens back" to Bush v. Gore in the 2000 election, when Chief Justice William Rehnquist and two other conservative justices "took the view that the Florida state court went too far when it ordered a partial recount of votes." Tuesday's ruling "vindicates the Rehnquist concurrence" of 23 years ago because instead of three votes for the Rehnquist proposition, there are now six justices who have embraced it, Hasen said. "I think that was the price that the liberal justices paid to get an opinion that rejected the most extreme version of this theory," he added.

Hasen predicts it won't be just the Supreme Court that gets these election cases. You can easily imagine election losers running to friendly lower-court judges, hoping for a second bite at the apple, he says. "I think it's going to create mischief," he said. "This is a time bomb waiting to explode."

But others disagree.

"I think there's going to be a lot of litigation," said University of Iowa law professor Derek Muller. "But I question how successful that litigation will be. I think there's a very low likelihood of success."

Others saw the decision as a clear defeat for the Independent State Legislature theory. The decision "was a resounding, reverberating victory for American democracy," said J. Michael Luttig, a former federal judge with decidedly conservative views who worked on the brief for Common Cause opposing the ISL theory.

"This is a very forceful repudiation of the premises of the independent state legislature idea," said University of Illinois law school dean Vikram Amar, who was among a group of liberal and conservative scholars who filed a brief in the case. "What this case does is it reaffirms the flexibility that states have to confer power in different institutions in a way that deals with the challenges confronted by modern democracy," he said.

Legacy of Bush v. Gore

Indeed, Chief Justice Roberts, in his opinion for the court, went out of his way to reaffirm a decision that he dissented from eight years ago, a decision that allows states to deal with the problem of partisan gerrymandering by creating independent redistricting commissions.

That said, there were lots of loose threads still hanging after Thursday's ruling. The Roberts opinion pointed to Chief Justice William Rehnquist's concurring opinion in Bush v. Gore, as well as the dissenters' different different views in the case. In the end, though, Roberts said: "We do not adopt these or any other test by which we can measure" state court interpretations of state election laws. We hold only that state courts may not transgress the ordinary bounds of judicial review."

In a separate concurring opinion for himself only, Justice Kavanaugh said that he saw little difference between the Rehnquist concurrence in Bush v. Gore and the opinion written by the dissenters in the case. Both, he said "convey essentially the same point." When federal courts review a state court's interpretation of state law, federal courts "should be deferential, but deference is not abdication."

And finally, while technically affirming the judgement of the North Carolina Supreme Court, the justices declined to say if the state court was right in its original decision. That decision was overturned earlier this year after Republicans retook control of the state supreme court.

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