District Judge Sarah Wallace issued the ruling on Friday, requiring that the Colorado secretary of state place Mr Trump on the state's primary ballot next year.

Section three of the 14th Amendment bars from office those who swore an oath to uphold the Constitution and then "engaged in insurrection" against it.A group of Colorado voters filed a legal challenge in September, arguing the amendment should apply to Mr Trump and his involvement in the 2021 riot at the US Capitol.

But Ms Wallace disagreed, arguing in her ruling that the 14th amendment's insurrection ban does not apply to presidents because Section 3 does not explicitly name them.

"After considering the arguments on both sides, the Court is persuaded that 'officers of the United States,' did not include the President of the United States."

"[I]t appears to the court that for whatever reason the drafters of Section Three did not intend to include a person who had only taken the presidential oath," she wrote in her ruling.

Ms Wallace did find, however, that Mr Trump "engaged in an insurrection on January 6, 2021 through incitement, and that the First Amendment does not protect Trump's speech".

The ruling is the latest setback for efforts to disqualify Mr Trump from the Republican primary election.

Similar lawsuits in New Hampshire, Minnesota and Michigan have already failed.

In a statement issued after the ruling, the left-leaning Citizens for Responsibility and Ethics in Washington - which filed the Colorado lawsuit - said it would be filing an appeal to the Colorado Supreme Court shortly.

The group applauded Ms Wallace's finding that Mr Trump had engaged in insurrection on 6 January.

"We are proud to have brought this historic case and know we are right on the facts and right on the law," the group said. "Today was not the end of this effort, but another step along the way."

It comes after a week-long bench trial, during which lawyers for the group of voters who filed the challenge argued Mr Trump had lost the right to run for president again because of his role in the 6 January Capitol riots. Lawyers for the plaintiffs called several witnesses, including two US Capitol Police officers who were injured during the riots.

Lawyers for Mr Trump, meanwhile, argued he did not bear responsibility for the attacks. They noted that similar legal challenges against the president have been unsuccessful.

"The petitioners are asking this court to do something that's never been done in the history of the United States," said Trump attorney Scott Gessler. "The evidence doesn't come close to allowing the court to do it."

The 14th Amendment was ratified after the American Civil War, and Section 3 was deployed to bar secessionists from returning to previous government posts once southern states re-joined the Union.

It was used against the likes of Confederate president Jefferson Davis and his vice-president Alexander Stephens, both of whom had served in Congress, but has seldom been invoked since.

The legal strategy has picked up steam since August, when Mr Trump was accused of election subversion in two separate criminal cases.

It is unclear if future challenges to Mr Trump's name on the ballot will emerge in Colorado or other states ahead of the Republican primary and the general election.

Legal experts believe the case - or another like it - is likely to end up before the US Supreme Court.