Former President Donald Trump cannot appear on the ballot in Colorado in next year’s presidential election because of his role in the Jan. 6, 2021, attack on the U.S. Capitol by his supporters, the state’s top court ruled Tuesday in a historic judgment that the U.S. Supreme Court will likely take up.

The 4-3 ruling from the Colorado Supreme Court makes Trump the first presidential candidate in U.S. history to be deemed ineligible for the White House under a rarely used provision of the U.S. Constitution that bars officials who have engaged in “insurrection or rebellion” from holding office.

The ruling applies only to Colorado’s March 5 Republican primary, but its conclusion could affect Trump’s status in the state for the Nov. 5 general election. Nonpartisan U.S. election forecasters view Colorado as safely Democratic, meaning President Joe Biden will likely carry the state regardless of Trump’s fate.

Trump vowed to appeal the ruling to the U.S. Supreme Court, and the Colorado court said it would delay the effect of its decision until at least Jan. 4, 2024, to allow for an appeal.

The ruling sets the stage for the U.S. Supreme Court, whose 6-3 conservative majority includes three Trump appointees, to consider whether Trump is eligible to serve another term as president.

The lawsuit is viewed as a test case for a wider effort to disqualify Trump from state ballots under section 3 of the 14th Amendment, enacted after the U.S. Civil War to keep supporters of the Confederacy from serving in the government.

The Colorado court concluded that the U.S. Constitution bars Trump, the frontrunner for the Republican nomination in 2024, from appearing on the ballot because of his role in instigating violence at the Capitol as lawmakers met to certify the results of the 2020 election. The court’s majority acknowledged the decision was “uncharted territory.”

“We do not reach these conclusions lightly,” the majority justices wrote. “We are mindful of the magnitude and weight of the questions now before us. We are likewise mindful of our solemn duty to apply the law, without fear or favour, and without being swayed by public reaction to the decisions that the law mandates we reach.”

Trump’s campaign called the court decision “undemocratic.”

“The Colorado Supreme Court issued a completely flawed decision tonight and we will swiftly file an appeal to the United States Supreme Court,” a spokesperson from the Trump campaign said.

The decision reverses a ruling by a lower court judge who found Trump engaged in insurrection by inciting his supporters to violence, but, concluded that as president, Trump was not an “officer of the United States” who could be disqualified under the amendment.

The Biden campaign declined to comment.

VICTORY FOR ADVOCACY GROUPS The case was brought by a group of Colorado voters, aided by the group Citizens for Responsibility and Ethics in Washington, who argued that Trump should be disqualified for inciting his supporters to attack the Capitol in a failed attempt to obstruct the transfer of presidential power to Biden after the 2020 election.

CREW President Noah Bookbinder said in a statement that the court’s decision is “not only historic and justified but is necessary to protect the future of democracy in our country.”

Courts have rejected several lawsuits seeking to keep Trump off the primary ballot in other states. Minnesota’s top court rebuffed an effort to disqualify Trump from the Republican primary in that state but did not rule on his overall eligibility to serve as president.

Some advocates had hoped the Colorado case would boost the overall disqualification effort and potentially put the issue before the U.S. Supreme Court.

Trump’s campaign has condemned 14th Amendment challenges as an attempt to deny millions of voters their preferred choice for president.

Trump’s lawyers mounted several defences in the case, arguing that Trump’s speech to supporters on the day of the riot was protected by his right to free speech, that the constitutional amendment does not apply to U.S. presidents and that Congress would need to vote to disqualify a candidate.

Three Colorado Supreme Court justices dissented from Tuesday’s ruling.

One of the dissenting justices, Carlos Samour, said in a lengthy opinion that a lawsuit is not a fair mechanism for determining Trump’s eligibility for the ballot because it deprives him of his right to due process, noting that a jury has not convicted him of insurrection.

“Even if we are convinced that a candidate committed horrible acts in the past - dare I say, engaged in insurrection - there must be procedural due process before we can declare that individual disqualified from holding public office,” Samour said.