Colorado's Supreme Court has removed Donald Trump from the 2024 presidential ballot, citing an insurrection clause in the US Constitution.
In a landmark decision that upends the White House race, the court ruled 4-3 that Mr Trump is not an eligible candidate because of section 3 of the 14th Amendment.
But the decision has been placed on hold pending appeal next month.
Several attempts to kick Mr Trump off the ballot in other states have failed.
Tuesday's decision does not apply to states outside of Colorado.
The top court wrote in its ruling: "We do not reach these conclusions lightly. 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 favor, and without being swayed by public reaction to the decisions that the law mandates we reach."
The decision reverses an earlier one from a Colorado judge, who ruled that the 14th Amendment's insurrection ban did not apply to presidents because the section does not explicitly name them.
That same lower court judge also found that Mr Trump had participated in an insurrection on the day of the US Capitol riot in 2021 when supporters of his stormed Congress as lawmakers were certifying President Joe Biden's election victory.
The Colorado Supreme Court's decision does not go into effect until at least 4 January 2024. That is the eve of the deadline for the state to print its presidential primary ballots.
In a statement, Steven Cheung, a spokesman for the Trump campaign, called the ruling "completely flawed" and lambasted the justices, who were all appointed by Democratic governors.
"Democrat Party leaders are in a state of paranoia over the growing, dominant lead President Trump has amassed in the polls," Mr 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."
Mr Cheung added that Mr Trump's legal team would "swiftly file an appeal" to the US Supreme Court.
Citizens for Responsibility and Ethics in Washington (CREW), a watchdog group that brought the case, welcomed the ruling.
"It is not only historic and justified, but is necessary to protect the future of democracy in our country," the group's president, Noah Bookbinder, said in a statement.
Similar lawsuits in New Hampshire, Minnesota and Michigan have failed.
The 14th Amendment was ratified after the American Civil War. Its Section 3 was intended to block secessionists from returning to previous government roles once southern states re-joined the Union.
It was used against Confederate president Jefferson Davis and his vice-president Alexander Stephens, both of whom had served in Congress, but has seldom been invoked since.
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