Updated March 4, 2024 at 11:12 AM ET

The U.S. Supreme Court restored Republican presidential front-runner Donald Trump to the Colorado primary ballot, ruling that the state lacked authority to disqualify him after his actions three years ago during the siege on the U.S. Capitol.

The unanimous decision came only weeks after the justices heard oral arguments in the politically sensitive case that put the high court in the middle of the 2024 presidential election. And it comes a week after the court said it would hear arguments in April in a case that seeks to answer whether Trump enjoys broad immunity for his actions on Jan. 6.

In a post on Truth, his social media platform, Trump called the Colorado opinion a "BIG WIN FOR AMERICA!!!" In remarks from his Florida resort a short time later, the former president said the high court decision "will go a long way in bringing our country together."

Six Colorado voters argued that Trump had run afoul of a post-Civil War law that bars people who took an oath to support the Constitution from engaging in an insurrection or rebellion. Section 3 of the 14th Amendment has never been used against a presidential candidate, and it's only been deployed eight times since the 1860s.

That sparse record contributed to the high court's decision Monday.

"Because the Constitution makes Congress, rather than the States, responsible for enforcing Section 3 against federal officeholders and candidates, we reverse," the court decision concluded.

The ruling made clear that lawmakers after the Civil War intended the 14th Amendment to expand federal power, at the expense of the states, and that the Constitution "empowers Congress" to determine how to use the "severe" penalty of disqualification.

While the justices came together to agree Trump could not be removed from the Colorado ballot, they differed as to how far they would go.

The three liberal-leaning justices, Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson, wrote to criticize the majority for deciding "momentous and difficult issues unnecessarily."

Those justices said the majority overreached when it set out ways Section 3 of the 14th Amendment should be enforced, basically creating what they called "a special rule for the insurrection disability."

Justice Amy Coney Barrett, who was appointed by Trump, wrote separately to say the court did not need to address "the complicated question whether federal legislation is the exclusive vehicle" to enforce the insurrection clause.

"The majority's choice of a different path leaves the remaining justices with a choice of how to respond," she wrote. "In my judgment this is not the time to amplify disagreement with stridency."

Barrett continued: "The Court has settled a politically charged issue in the volatile season of a Presidential election. Particularly in this circumstance, writings on the Court should turn the national temperature down, not up."

The ultimate ruling is not much of a surprise following oral argument. Jason Murray, the lawyer for the voters, ran into rough territory at the Supreme Court, where justices across the ideological spectrum tossed difficult questions his way.

"What about the idea that we should think about democracy?" asked Justice Brett Kavanaugh, who was appointed by Trump. "Because your position has the effect of disenfranchising voters to a significant degree."

"I think the question that you have to confront is why a single state should decide who gets to be president of the United States," said Kagan, an Obama appointee.

Chief Justice John Roberts said he could foresee, in the not-too-distant future, a world in which some states would try to boot the Democratic nominee from the ballot, and others would use Section 3 to do the same for the Republican candidate.

"It will come down to just a handful of states that are going to decide the presidential election," Roberts said. "That's a pretty daunting consequence."

The case has been closely watched by legal experts and election administrators across the nation. Many of them had filed friend-of-the-court briefs asking the justices to rule swiftly, and decisively, before millions more American voters head to the polls.

Janai Nelson, president of the NAACP Legal Defense Fund, said the court majority had ignored the plain text of the 14th Amendment, effectively giving "constitutional immunity to insurrectionists, absent legislation from Congress."

The question about Trump's disqualification in Colorado has been playing out in different ways in dozens of other states. Maine's secretary of state found that Trump is disqualified from appearing on Maine's primary ballot, but the decision was stayed pending Trump's appeal. A judge in Illinois also barred Trump but paused her ruling pending action from the Supreme Court.

Derek Muller, an election law professor at Notre Dame, said in a statement the Supreme Court decision "shuts the door on any exclusion of Trump from the ballot in any state, either in the primary or the general."

Jonathan Mitchell, a lawyer for Trump, made a series of arguments to keep the former president on the ballot. Among them: Trump is not covered by that part of the Constitution because he took a different oath of office, and that Congress would need to act, and answer key questions about disqualification, before any candidate could be removed from the ballot.

But Murray, the lawyer for the Colorado voters, pushed back at that idea.

"Those who drafted Section 3 of the 14th Amendment back in the 1860s were very clear that they understood this provision not just to cover former Confederates but that it would stand as a shield to protect our Constitution for all time going forward, and so this is not some dusty relic," he said.

Noah Bookbinder, the president of Citizens for Responsibility and Ethics in Washington, a nonprofit group that backed the legal challenge to Trump, pointed out the Supreme Court did not erase fact-finding by judges in Colorado that Trump had engaged in an "insurrection."

"Every court–or decision-making body–that has substantively examined the issue has determined that January 6th was an insurrection and that Donald Trump incited it," Bookbinder said. "That remains true today."

In his remarks at his Mar-a-Lago resort Monday, Trump accused President Biden — without offering any evidence — of weaponizing the Justice Department against him. The two men are likely to face off in the November presidential election.

"Fight your fight yourself," Trump said. "Don't use prosecutors and judges to go after your opponent."

There is no evidence — none — that the White House is coordinating with prosecutors who are targeting Trump. Indeed, the U.S. Justice Department operates independently of the White House.

NPR legal intern Elissa Harwood contributed to this report.

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