A Colorado court began hearing a lawsuit on Monday that seeks to bar Donald Trump from the 2024 presidential ballot on the grounds he violated his oath of office by engaging in an insurrection.

The case, one of several similar legal efforts to keep the former president out of the running, is likely to eventually end up before the United States Supreme Court, where conservatives hold a 6-3 majority.

The lawsuit filed in Colorado by Citizens for Responsibility and Ethics, a Washington-based watchdog group, claims Trump is ineligible to run for the White House again because of the 6 January 2021 attack on the US Capitol by his supporters.

The argument, which has legal scholars sharply divided, rests on an amendment to the Constitution ratified after the 1861-65 Civil War.

Section 3 of the 14th Amendment bars anyone from holding public office if they engaged in "insurrection or rebellion" after once pledging to support and defend the Constitution.

The amendment, ratified in 1868, was aimed at preventing supporters of the slave-holding Confederacy from being elected to Congress or from holding federal positions.

Acting on behalf of six Colorado voters, CRE petitioned the Colorado secretary of state, the top election official in the western state, to keep Trump off the ballot in next year's presidential election.

"Trump incited a violent mob to attack our Capitol to stop the peaceful transfer of power under our Constitution," Eric Olson, an attorney for CRE, said in his opening argument at the livestreamed hearing being held in Denver before Judge Sarah Wallace.

"January 6 was an insurrection against the Constitution," Olson said. "Trump engaged in that insurrection."

"We are here because Trump claims that after all that, he has the right to be president again," he said. "But our Constitution, our shared charter of our nation, says he cannot do so."

Scott Gessler, a former Colorado secretary of state representing Trump, countered that the suit was "anti-democratic" and urged the judge to throw it out.

"When it comes to decide who should lead our nation, it's the people of the United States of America that gets to make those decisions," Gessler said. "We have elections."

"This is a case of lawfare that seeks to interfere with the presidential election," he said.

'Election interference'

The Minnesota Supreme Court is to hear a similar case on Thursday in which several voters are seeking to bar Trump from the ballot in the northern state.

According to CRE, eight public officials have been disqualified under Section 3 of the 14th Amendment since 1868 but only one in recent times, a New Mexico county commissioner who was removed from office over his role in the 6 January attack on the Capitol.

The 77-year-old Trump is to go on trial in Washington in March on charges of conspiring to overturn the results of the November 2020 election won by Democrat Joe Biden.

He faces similar charges in a separate case in the southern state of Georgia.