Washington — The Supreme Court on Tuesday rejected a controversial theory that would have given state lawmakers unfettered power to set the rules for federal elections in their states, ruling that the so-called "independent state legislative theory" is inconsistent with the Constitution.

In declining to embrace the idea, which stems from an interpretation of the Constitution's Elections Clause, the court left in place a key check on state lawmakers' authority over how federal elections in their states are conducted and their drawing of congressional maps.

The decision is a major victory for voting rights advocates, who feared that a ruling adopting the independent legislature theory would wreak havoc on election systems, and allow state legislatures to operate unchecked when setting federal election rules and drawing voting lines.

Chief Justice John Roberts authored the opinion for the 6-3 majority in the case known as Moore v. Harper, which stems from a dispute in North Carolina. The court ruled that the Supreme Court has jurisdiction to review an opinion by the North Carolina Supreme Court against state Republican officials, and said the Constitution's Elections Clause does not grant exclusive and independent authority in state legislatures to set the rules regarding federal elections.

"State courts retain the authority to apply state constitutional restraints when legislatures act under the power conferred upon them by the Elections Clause," Roberts wrote. He was joined by Justices Sonia Sotomayor, Elena Kagan, Brett Kavanaugh, Amy Coney Barrett and Ketanji Brown Jackson.

"The Elections Clause does not insulate state legislatures from the ordinary exercise of state judicial review," Roberts wrote. The Elections Clause states: "the Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof."  

Though the court concluded that the clause "does not exempt state legislatures from the ordinary constraints imposed by state law," Roberts noted that state courts "do not have free rein." 

"We hold only that state courts may not transgress the ordinary bounds of judicial review such that they arrogate to themselves the power vested in state legislatures to regulate federal elections," the chief justice wrote, meaning that state courts can't overstep and assume the powers granted to the legislatures under the Constitution.

Justices Clarence Thomas, Neil Gorsuch and Samuel Alito dissented, with Thomas writing for the trio that the question before the Supreme Court was moot and the case should be dismissed.

Vice President Kamala Harris reiterated the Biden administration's efforts to secure access to the ballot box and urged Congress to pass legislation that protects voting rights.

"Voting is the bedrock of our democracy," she said in a statement. "Today's decision preserves state courts' critical role in safeguarding elections and protecting the voice and the will of the American people. We know that more work must to be done to protect the fundamental right to vote and to draw fair maps that reflect the diversity of our communities and our nation."

Abha Khanna, a lawyer who represented the North Carolina plaintiffs, cheered the Supreme Court's decision as a win for free and fair elections. 

"In its most extreme form, the Independent State Legislature Theory could have weakened the foundation of our democracy, removing a crucial check on state legislatures and making it easier for rogue legislators to enact policies that suppress voters and subvert elections without adequate oversight from state court," she said in a statement. "We are incredibly relieved that the Supreme Court decisively rejected this dangerous theory."

The theory that state legislatures have exclusive authority to set presidential and congressional elections rules without oversight from state courts lay largely dormant for more than 15 years. The concept regained attention after the 2020 presidential election, when then-President Donald Trump's allies raised it as part of efforts to reverse the outcome.

Moore v. Harper arose from the redrawing of North Carolina's congressional map by state Republican legislative leaders after the 2020 Census. The state supreme court invalidated the voting boundaries, finding in a February 2022 decision that they were an unconstitutional partisan gerrymander. 

After a state trial court rejected new congressional voting lines drawn by the GOP-controlled General Assembly, it adopted a map drawn by a group of special masters, to be used only for the 2022 election cycle.

North Carolina Republicans asked the Supreme Court to intervene, arguing that under the Elections Clause, state courts did not have the authority to change rules governing the "times, place and manner" of federal elections. By allowing the court-crafted map to be used, they said, the state's judiciary had decided the "manner" in which North Carolina's congressional elections would be held, usurping the power granted to the state legislature. 

Months after the Supreme Court heard arguments in the case, the North Carolina Supreme Court reconsidered part of the February 2022 decision that the justices were reviewing. In March, the Supreme Court asked the parties involved — North Carolina GOP legislators, voting rights groups and voters, state election officials and the Biden administration — to submit additional briefs explaining whether it still had the power to decide the case, raising questions of whether the justices would decide the dispute after all.

Then, in late April, the state supreme court's Republican majority overturned the earlier February 2022 ruling that invalidated congressional voting lines drawn by state GOP lawmakers. The ruling from North Carolina's high court effectively gives state lawmakers the green-light to draw its congressional map to favor GOP candidates. 

In finding that the Supreme Court has jurisdiction to review the state high court's decision — which said the GOP-crafted congressional redistricting plan was unlawful — Roberts said the subsequent state court action in recent months does not render the case moot.

"Although partisan gerrymandering claims are no longer viable under the North Carolina Constitution, the North Carolina Supreme Court has done nothing to alter the effect of the judgment in Harper I enjoining the use of the 2021 maps. As a result, the legislative defendants' path to complete relief runs through this Court," he wrote. Harper I is the North Carolina Supreme Court's February 2022 decision.

Before the court agreed to take up the appeal from North Carolina Republicans, the three justices who ultimately dissented — Alito, Thomas and Gorsuch — expressed support for the independent state legislature theory. A fourth, Kavanaugh, urged the Supreme Court to consider the issue.

In an opinion concurring with the court's judgment, Kavanaugh said the majority "correctly concludes" that state laws governing federal elections are subject to review by state courts, including to ensure they comply with state constitutions.