Efforts to use the U.S. Constitution's “insurrection” clause to bar former President Donald Trump from running for the White House again entered a new phase Monday in a hearing focused on whether the Jan. 6 Capitol attack meets the Constitution's definition of the word and whether Trump's role meets the threshold for being barred.

The Colorado hearing is the first of two states' lawsuits that could end up reaching the U.S. Supreme Court.

Monday’s testimony began with details about the 2021 assault that was intended to halt certification of Joe Biden's election win.

Attorney Eric Olson, representing a group of Colorado voters seeking to keep Trump off the ballot, recounted Trump’s violent rhetoric and encouraging of a crowd that came within “40 feet” of the vice president when they stormed the Capitol. He said Trump “summoned and organized the mob.”

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

At the start of Monday's hearing in Colorado, the judge rejected a Trump motion that she step aside because she once contributed money to a liberal group.

On Thursday, oral arguments are scheduled before the Minnesota Supreme Court on an effort to kick the Republican former president off the ballot in that state. Whether the judges keep Trump on the ballots or boot him, their rulings are likely to be swiftly appealed, eventually to the U.S. Supreme Court. The nation's highest court has never ruled on the Civil War-era provision in the 14th Amendment that prohibits those who swore an oath to uphold the Constitution and then “engaged in insurrection” against it from holding higher office.

“We've had hearings with presidential candidates debating their eligibility before — Barack Obama, Ted Cruz, John McCain,” said Derek T. Muller, a Notre Dame law professor, listing candidates challenged on whether they met the constitutional requirement of being a “natural born citizen.” But these cases, Muller added, are different from using an obscure clause of the Constitution with the “incendiary” bar against insurrection.

Even if they're long shots, Muller said, they have a plausible legal path to success and raise important issues.

“Those legal questions are very heavy ones,” Muller said.

Dozens of cases citing Section Three of the 14th Amendment have been filed in recent months, but the ones in Colorado and Minnesota seem the most important, according to legal experts. That's because they were filed by two liberal groups with significant legal resources. They also targeted states with clear, swift processes for challenges to candidates' ballot qualifications.

That means the Colorado and Minnesota cases are taking a more legally sound route to get courts to force election officials to disqualify Trump, as opposed to other lawsuits that seek a sweeping ruling from federal judges that Trump is no longer eligible for the presidency.

The plaintiffs in the cases argue the issue is simple: Trump's efforts to overturn his 2020 election loss, leading to the Jan. 6, 2021, attack on the U.S. Capitol, mean he's disqualified from the presidency just as clearly as if he were not a natural-born citizen, another constitutional prerequisite for the office.

“Four years after taking an oath to ‘preserve, protect and defend’ the Constitution as President of the United States ... Trump tried to overthrow the results of the 2020 election, leading to a violent insurrection at the United States Capitol to stop the lawful transfer of power to his successor,” alleges the Colorado lawsuit, filed on behalf of Republican and unaffiliated voters by the liberal group Citizens for Responsibility and Ethics in Washington.

“By instigating this unprecedented assault on the American constitutional order, Trump violated his oath and disqualified himself under the Fourteenth Amendment from holding public office, including the Office of the President.”

Trump has castigated the lawsuits as “election interference.” His lawyers contend that none of the issues are simple in a provision of the Constitution that hasn't been used in 150 years.

“This is a legal Hail Mary by the Democrats,” said Mike Davis, an attorney who appeared with representatives of the Trump campaign outside court Monday in Denver before the Colorado trial got started. “This case is going to fail.”

Trump's campaign said it had filed a motion for the judge in the case, Sarah B. Wallace, to recuse herself because she had made a $100 donation in October 2022 to the Colorado Turnout Project, a liberal group whose website says it was formed to “prevent violent insurrections” such as the Jan. 6 attack.

She was appointed to the bench in August of that year by Gov. Jared Polis, a Democrat. Wallace denied the motion, saying she didn’t recall the donation until the motion was filed and has no preconceptions about the legal issues in the case.

“I will not allow this legal proceeding to turn into a circus,” she said as the hearing began.

The clause in the 14th Amendment has only been used a handful of times since immediately after the Civil War. Trump's lawyers contend that it was never meant to apply to the office of president, which is not mentioned in the text, unlike “Senator or Representative in Congress” and “elector of President and Vice President.”

The provision allows Congress to grant amnesty — as was done in 1872 to allow former confederates back into government — which has led some to argue that it has no power without an enabling act of Congress.

Finally, Trump's lawyers contend the former president never “engaged in insurrection” and was simply exercising his free speech rights to warn about election results he did not believe were legitimate.

“Trump’s comments did not come close to ‘incitement,’ let alone ‘engagement’ in an insurrection,” his attorneys wrote in a filing in the Colorado case, adding examples of cases where the congressional authors of Section Three declined to use it against people who only rhetorically backed the confederacy.

The arguments in Colorado could feature testimony from witnesses to the Jan. 6 attack or other important events during Trump's efforts to overturn the election. The identities of witnesses have been shielded until they take the stand, part of the court's effort to limit the heated rhetoric and threats that have become an issue in Trump's criminal trials.

The lawyers are expected to delve deeply into the history of the drafting of the provision in the 14th Amendment and its use between its adoption in 1868 and the amnesty law in 1872. There is scant legal precedent on the issue — so little that the attorneys have had to argue about the meaning of an 1869 case written by Salmon Chase, who was then chief justice of the U.S. Supreme Court but wrote only as an appeals judge.

After the amnesty act in 1872, legal scholars could only find one other time the provision was cited, when Congress refused to seat a socialist member of the House of Representatives because he opposed entry into World War I.

Then last year, it was used by CREW to bar the head of “Cowboys for Trump” from a county commission seat in rural New Mexico. A second liberal group, Free Speech For People, filed lawsuits seeking to prevent Republican Reps. Marjorie Taylor-Greene and Madison Cawthorn from running for reelection.

The judge overseeing Greene’s case ruled in her favor, while Cawthorn’s case became moot after he was defeated in his primary. Free Speech For People filed the case in Minnesota, where challenges to ballot appearances go straight to the state supreme court.