Donald Trump is ineligible to run for president in 2024 because of the Jan. 6 riot at the U.S. Capitol, the Colorado Supreme Court ruled on Tuesday.
The historic decision based on the 14th Amendment, barring Trump from the presidential primary ballot, sets up a battle before the nation's highest court about the fate of next year's election.
In a 4-3 ruling that will soon be appealed -- and that is likely to inspire fierce criticism from Trump's supporters and vocal applause from those who have condemned his behavior around Jan. 6 -- a majority of Colorado's seven justices wrote that the former president "engaged in insurrection."
"President Trump's direct and express efforts, over several months, exhorting his supporters to march to the Capitol to prevent what he falsely characterized as an alleged fraud on the people of this country were indisputably overt and voluntary," the justices wrote.
"Moreover," they wrote, "the evidence amply showed that President Trump undertook all these actions to aid and further a common unlawful purpose that he himself conceived and set in motion: prevent Congress from certifying the 2020 presidential election and stop the peaceful transfer of power."
In light of this, the ruling states, "[W]e conclude that because President Trump is disqualified from holding the office of President under Section Three, it would be a wrongful act under the Election Code for the Secretary to list President Trump as a candidate on the presidential primary ballot."
The justices stayed their ruling until Jan. 4, pending appeal.
Three of the judges dissented: Chief Justice Brian D. Boatright and Justices Carlos A. Samour Jr. and Maria E. Berkenkotter.
MORE: Why are the 14th Amendment lawsuits seeking to bar Trump failing?Boatright, in his dissent, wrote that the "absence of an insurrection-related conviction" against Trump should have called for the case to be dismissed.
Samour wrote that the majority's opinion "flies in the face of the due process doctrine."
The ruling follows a monthslong challenge in Colorado to Trump's ballot eligibility under Section 3 of the 14th Amendment, a Civil War-era constitutional clause that deems former office-holders ineligible from holding office again if they took an oath to support the Constitution and then engaged in "insurrection or rebellion" against the U.S.
In September, a Washington, D.C.-based watchdog group, Citizens for Responsibility and Ethics (CREW), filed a lawsuit on behalf of six Republican and unaffiliated voters in Colorado that claimed Trump had breached that clause due to his actions surrounding the Jan. 6, 2021, Capitol attack.
He has long denied any wrongdoing and was acquitted by Senate Republicans in 2021 after being impeached for allegedly inciting Jan. 6.
The Colorado Supreme Court's majority on Tuesday reversed a lower court's decision that the president was not an "officer" of the U.S. under the Constitution and therefore Section 3 of the 14th Amendment did not apply.
The ruling also denied Trump's appeal on 11 issues and found that his actions on Jan. 6, including a speech outside the White House that morning, were not protected by the First Amendment.
Trump, currently the front-runner in the 2024 GOP primary, has attacked the Colorado 14th Amendment challenge -- and similar such lawsuits against him around the country -- as baseless and anti-democratic.
A Trump spokesman on Tuesday night soon vowed an appeal and the campaign has already begun fundraising off of the decision.
"The Colorado Supreme Court issued a completely flawed decision tonight .... We have full confidence that the U.S. Supreme Court will quickly rule in our favor and finally put an end to these unAmerican lawsuits," spokesman Steven Cheung said in a statement, in part.
CREW lauded the ruling as "necessary to protect the future of democracy in our country."
Norma Anderson, one of the six petitioners and a former Republican state lawmaker, said in a statement issued by CREW that "my fellow plaintiffs and I brought this case to continue to protect the right to free and fair elections enshrined in our Constitution and to ensure Colorado Republican primary voters are only voting for eligible candidates. Today's win does just that."
Trump has so far faced multiple 14th Amendment challenges in various states after the argument against his eligibility built momentum this year among advocates and in some legal circles, including with some conservative scholars.
But of the dozens of challenges to his candidacy, no court had yet disqualified him -- until Tuesday.
Lawsuits citing the 14th Amendment were dismissed by nine courts: in Michigan, by the district court in Colorado -- leading to the appeals battle there -- and by the Minnesota Supreme Court, a district court in Washington and by federal courts in Arizona, Rhode Island, New Hampshire and Florida.
On Dec. 6, the Colorado Supreme Court heard oral arguments in an appeal of the lower court judge's ruling rejecting CREW's challenge to Trump's ballot eligibility.
During a two-hour hearing in Denver, the seven-justice court posed sharp questions central to the case, including about the definition of insurrection; whether the Capitol riot was an insurrection; and whether the "insurrectionist ban" applies to a U.S. president.
"I guess I'm expressing a concern about the definition of insurrection that the district court adopted. It strikes me as somewhat or potentially broad -- so let me ask you to address that," Chief Justice Boatright said during the hearing.
The lower court judge in Colorado, Sarah B. Wallace, had ruled in November that while Trump was eligible to run in the 2024 race under the 14th Amendment, she found that he did engage in the Jan. 6 insurrection because he incited it.
Both CREW's legal team and Trump's lawyers appealed to the Colorado Supreme Court: CREW because of the final decision on Trump's ballot eligibility, and Trump's team over Wallace's opinion that he engaged in insurrection.
The attorney leading another set of disqualification challenges against Trump previously told ABC News that there was a "very good chance" a top court in Minnesota, Colorado or Michigan would rule on the issue before the end of the year -- teeing up urgent review by the U.S. Supreme Court.
"This question needs to be decided ideally before any ballots are printed, and I hope and expect it will be decided in our favor," Ben Clements, chairman and senior legal adviser of Free Speech for People, said in November.
An ABC News/Washington Post poll in September found mixed views on whether Trump should be allowed to run in 2024.
Forty-four percent of Americans said Trump should be barred from the presidency under the 14th Amendment; 50% said he should not be barred; and 6% had no opinion.
ABC News' Devin Dwyer, Lalee Ibssa, Soo Rin Kim, Gary Langer and Kendall Ross contributed to this report.