The Colorado Supreme Court has disqualified former US president Donald Trump from the ballot in the state’s presidential election next year over his role in the January 6, 2021, attack on the US Capitol by his supporters.

The ruling on Tuesday (local time) makes Trump the first presidential candidate in US history to be deemed ineligible for the White House under a rarely used provision of the US Constitution that bars officials who have engaged in “insurrection or rebellion” from holding office.

The court concluded that the US Constitution bars the frontrunner for the Republican presidential nomination in 2024 from appearing on the ballot because of his role instigating violence against the US government.

The ruling applies only to the state’s March 5 Republican primary. But its conclusion would likely also affect Trump’s status for the November 5 general election.

Non-partisan US election forecasters view Colorado as safely Democratic, meaning that President Joe Biden will likely carry the state regardless of Trump’s fate.

The case was brought by a group of Colorado voters, aided by the group Citizens for Responsibility and Ethics in Washington. They 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.

Citizens for Ethics spokesman Noah Bookbinder posted on social media that the decision was “a huge moment for democracy.”

But Trump’s campaign lashed it as “flawed” and “undemocratic”.

“We will swiftly file an appeal to the United States Supreme Court and a concurrent request for a stay of this deeply undemocratic decision,” spokesman Steven Cheung said.

He accused the “Democrat-appointed” panel of doing the bidding of a “[George] Soros-funded, left-wing group’s scheme to interfere in an election on behalf of Crooked Joe Biden”.

“Democrat Party leaders are in a state of paranoia over the growing, dominant lead President Trump has amassed in the polls,” Cheung said.

“They have lost faith in the failed Biden presidency and are now doing everything they can to stop the American voters from throwing them out of office next November.”

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

The decision is a victory for advocacy groups and anti-Trump voters who have mounted several similar legal challenges to Trump’s candidacy under Section 3 of the 14th Amendment, which was enacted after the Civil War.

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

A lawyer for Trump argued that the riot at the Capitol was not serious enough to qualify as an insurrection and that Trump’s remarks to his supporters in Washington that day were protected by his right to free speech.

The lawyer contended that courts had no authority to order Trump removed from the ballot.

Advocates have hoped to use the case to boost a wider disqualification effort and potentially put the issue before the US Supreme Court.

The US Supreme Court’s 6-3 conservative majority includes three Trump appointees.

The Colorado court said the ruling was stayed until January 4, 2024, to allow for appeals.

“The court’s decision today affirms what our clients alleged in this lawsuit: that Donald Trump is an insurrectionist who disqualified himself from office under Section 3 of the 14th Amendment based on his role in the January 6th attack on the Capitol, and that Secretary Griswold must keep him off of Colorado’s primary ballot,” CREW president Noah Bookbinder said.

“It is not only historic and justified, but is necessary to protect the future of democracy in our country.”

-with AAP