A government watchdog group filed a lawsuit on Wednesday seeking to bar Donald Trump from the 2024 presidential ballot on the grounds he violated his oath of office by engaging in an insurrection.

The lawsuit, filed in Colorado by the Washington-based Citizens for Responsibility and Ethics (CREW), rests on an amendment to the US 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, CREW petitioned elections officials in the western state to keep Trump off the ballot in next year's presidential election.

"Donald Trump tried to overthrow the results of the 2020 presidential election," the suit says.

"His efforts culminated on January 6, 2021, when he incited, exacerbated, and otherwise engaged in a violent insurrection at the United States Capitol.

"Because Trump took these actions after he swore an oath to support the Constitution, Section 3 of the Fourteenth Amendment prohibits him from being President and from qualifying for the Colorado ballot for President in 2024," the suit says.

Similar legal efforts to bar Trump from the ballot using the 14th Amendment are underway in several other states and could ultimately land at the US Supreme Court, where conservatives make up a 6-3 majority.

According to CREW, 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 January 6 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.

Trump was impeached for a second time by the House of Representatives after the attack on the Capitol -- he was charged with inciting an insurrection -- but was acquitted by the Senate.

- 'Betray their oaths' -

The argument that Trump should be ineligible to run again for president has been advanced by a number of legal experts, notably J. Michael Luttig, a conservative former US Court of Appeals judge, and Laurence Tribe, a professor of constitutional law at Harvard.

In an article published last month in The Atlantic, Luttig and Tribe argued that a criminal conviction was not needed to bar Trump from holding office again.

"The disqualification clause operates independently of any such criminal proceedings and, indeed, also independently of impeachment proceedings and of congressional legislation," they said.

"The clause was designed to operate directly and immediately upon those who betray their oaths to the Constitution, whether by taking up arms to overturn our government or by waging war on our government by attempting to overturn a presidential election through a bloodless coup."

Trump's efforts to reverse his 2020 presidential election loss and the eventual storming of the US Capitol by his supporters, the legal experts said, "place him squarely within the ambit of the disqualification clause.

"He is therefore ineligible to serve as president ever again," they added.

Trump, in a recent post on his Truth Social platform, hit back at the efforts to remove him from the presidential ballot, saying they had "no legal basis."

"Like Election Interference, it is just another 'trick' being used by the Radical Left Communists, Marxists, and Fascists, to again steal an Election," he said.