Washington — When the nine members of the Supreme Court take their seats on the bench on Thursday, they will be wading into uncharted legal waters to hear a case that could have sweeping ramifications for the 2024 presidential race.

The dispute before the court involves whether former President Donald Trump is ineligible for a second term in office because of his conduct surrounding the Jan. 6, 2021, assault on the U.S. Capitol. A decision against him could disrupt his bid for a second term in the White House. The outcome of the legal battle is expected to reverberate across all 50 states, since it could provide clarity about Trump's eligibility for the primary and general election ballots. 

The crux of the case, which arose out of a lawsuit six Colorado voters filed in the fall, is a seldom-used provision of a constitutional amendment passed in 1868 that was designed to keep former Confederates from holding public office.

Known as the insurrection clause, Section 3 of the 14th Amendment had never in the nation's history been used to disqualify a presidential candidate. That changed in December, when the Colorado Supreme Court concluded that Trump's conduct related to Jan. 6 deemed him ineligible for the presidency. The court ordered him to be excluded from the state's GOP presidential primary ballot.

That landmark decision was the catalyst for the high-stakes showdown now before the Supreme Court, which includes three justices appointed by Trump himself. The case, formally known as Trump v. Anderson, raises a number of untested legal questions for the justices to consider and propels the nation's highest court into a politically fraught dispute just as millions of voters prepare to cast their ballots for the 2024 presidential election. 

Not since its ruling in Bush v. Gore in 2000 has the Supreme Court been so squarely in the center of a presidential election.

"It just doesn't happen very often where you have a provision of the Constitution that is unknown, in some sense, from the point of view of the Supreme Court," Gerard Magliocca, an expert in Section 3, told CBS News. "Then you say well, it's about a former president who is running for president and so on — that gives it this added dimension which really has no counterpart that I can think of."

Why are Colorado voters challenging Trump's ballot eligibility?

The case before the Supreme Court was brought by the watchdog group Citizens for Responsibility and Ethics in Washington on behalf of four Republican and two unaffiliated voters in Colorado in September 2023. The voters argued that Trump is disqualified from holding the presidency under Section 3 and should be excluded from the Colorado primary and general election ballots.

Section 3 bars an individual who swore an oath to support the Constitution and then engaged in insurrection against it from holding federal or state office. Trump, the voters claimed, instigated the Jan. 6 attack as part of his efforts to thwart the peaceful transfer of presidential power after the 2020 election, and therefore is ineligible for a second term.

"If you decide you're going to undermine your oath, inflame your supporters, make all kinds of allegations that put election workers in harm's way, and then you foment an attack on the Capitol to stop the peaceful transfer of power, if you do things like that, you don't get to run again," said Krista Kafer, a Denver Post columnist and one of the Republican voters who signed on to the lawsuit.

After a five-day trial in Denver, District Judge Sarah B. Wallace determined that the events of Jan. 6 satisfied the definition of insurrection, and concluded Trump engaged in insurrection through incitement — the first time any judge had reached such a conclusion about the former president's conduct. But Wallace also ruled that Trump should be listed on the Colorado primary ballot because Section 3 does not apply to the presidency and the former president.

The Colorado voters and Trump appealed to the state supreme court, composed of seven justices appointed by Democratic governors. In December, that court issued a 4-3 decision finding that Trump is ineligible for the White House, reversing the district court's reasoning about the scope of Section 3.

"We do not reach these conclusions lightly. We are mindful of the magnitude and weight of the questions now before us," the majority wrote. "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."

Trump appealed the decision to the U.S. Supreme Court. He and the group of voters urged the justices to take up and decide the question of his eligibility swiftly. On Jan. 5, the high court agreed to consider whether the Colorado Supreme Court erred.

"You've got to protect our democracy, because you'll lose it if you don't take care of it," said Norma Anderson, the lead plaintiff in the case.

Anderson, 91, led a long career as a Republican in the Colorado legislature and was the first woman to serve as majority leader in both of its chambers. She recalled crying on Jan. 6 as she watched the mob of Trump's supporters breach the U.S. Capitol. She said Section 3 came to mind as she watched the events of that day unfold.

"You just don't try to overthrow an election in the United States, and that's what he did," Anderson said.

The arguments in the Trump Supreme Court case

Trump's appeal pushes the Supreme Court into new territory, as it has never before ruled directly on the application of the 155-year-old clause. 

His lawyers are asking the justices to consider a number of issues, including whether the provision applies to Trump as a former president; whether he engaged in insurrection; and whether state and federal courts can even enforce Section 3 without legislation from Congress. They also argue that the provision cannot be used to deny Trump access to the ballot because Section 3 prohibits a person only from holding office, not running as a candidate or winning election.

The Supreme Court only needs to side with the former president on any one of these matters for Trump to prevail.

"The court should put a swift and decisive end to these ballot-disqualification efforts, which threaten to disenfranchise tens of millions of Americans and which promise to unleash chaos and bedlam if other state courts and state officials follow Colorado's lead and exclude the likely Republican presidential nominee from their ballots," his lawyers told the justices in their opening brief.

In addition to Colorado, the secretary of state in Maine determined that Trump is barred from holding office and should be excluded from the primary ballot. A state court, though, paused that decision and ordered the secretary to reconsider her finding once the Supreme Court rules.

Section 3 says that it applies to those who have taken a constitutional oath "as a member of Congress, or as an officer of the United States, or as a member of any State legislature, or as an executive or judicial officer of any State." The primary argument from Trump's legal team is that he is not subject to the provision because the president is not an "officer of the United States." 

His lawyers argued that the president is excluded from the three other instances where the term appears in the Constitution, and the insurrection clause itself does not mention the president or the presidency.

"To accept the Colorado Supreme Court's assertion that section 3 includes the presidency, one must conclude that the drafters decided to bury the most visible and prominent national office in a catch-all term that includes low-ranking military officers, while choosing to explicitly mention presidential electors," Trump's lawyers wrote. "This reading defies common sense."

Section 3 also says that oath-taking insurrectionists cannot serve in Congress, become a presidential or vice presidential elector or hold "any office, civil or military, under the United States." Trump's legal team argues that there is not clear evidence the presidency fits that definition.

But Magliocca, who testified as an expert witness on the history of Section 3 in the Colorado trial, argued that it created another constitutional qualification for the presidency, like the age, citizenship and residency requirements for lawmakers and the president found elsewhere in the founding document.

"There's nothing about the history or text of Section 3 that would say there's anything special about the presidency that makes it exempt, and it would make a hash of the other limitations that the Constitution places on who can be president," he said.

Trump's lawyers have asserted that as president, he swore an oath to "preserve, protect and defend" the Constitution, not "support" it, as Section 3 says. Because Trump did not hold public office before he was elected in 2016, he never took an oath to "support" the Constitution, their argument goes.

The voters, though, said that the presidential oath is more demanding, and noted that Trump's interpretation of Section 3 effectively creates an exception that applies only to him.

"Every other president in our country's history has taken an oath to support the Constitution, but Trump's theory is that political neophytes like him who have only taken the presidential oath, and only those political neophytes, fall outside Section 3's scope, which is the definition of a loophole to say that in our 250-year history, this rule applies to everyone but him," said Eric Olson, a lawyer who is representing the Colorado voters.

Trump is currently the front-runner for the Republican presidential nomination and won the Iowa caucuses and New Hampshire primary, the first two contests of the nomination process. Since Trump is likely to become the GOP nominee, his lawyers told the Supreme Court, the justices should "protect the rights of the tens of millions of Americans who wish to vote" for him.

Olson, though, reiterated that voters often are confronted with limits on who can serve as president. While Taylor Swift may be immensely popular and her fans may want her in the White House, he said, she is only 34 years old, and the Constitution requires the president to be at least 35.

"This notion somehow that it would 'deprive people of who they want to vote for' is a shorthand for disregarding the Constitution," Olson said. "More importantly, having a threat of bedlam used as an argument as to why one side or the other should win is not how the rule of law works in this country."

Trump's legal team also claimed that Section 3 is a prohibition only on holding office and does not bar a person from merely running for the White House. Congress can also waive the prohibition on holding office with a two-thirds vote. No court or litigant, they claim, can declare that Trump is "presently" disqualified from holding office without assuming that Congress will refuse to grant him a waiver.

"Anderson may believe or hope that Congress will not waive section 3 between now and January 20, 2029," Trump's lawyers wrote. "But neither the Colorado Supreme Court nor this court can declare a candidate ineligible for the presidency now based on a prediction of what Congress may or may not do in the future."

Press Millen, a North Carolina-based attorney who represented a group of voters who challenged former Rep. Madison Cawthorn's candidacy for the House under Section 3, warned that the argument that it's too soon to enforce the provision creates a "potential disaster scenario."

"It's a recipe for a disaster and another coup attempt, potentially," he said. "It doesn't make a lot of sense, the idea that I can run and you can't exclude me from the ballot but I can't hold the office."

Colorado Secretary of State Jena Griswold, who is urging the Supreme Court to uphold the state high court's decision, said states have for decades had a role in ensuring only eligible candidates are listed on their ballots. 

"For over 100 years, we've made determinations as to whether someone was too young, not a resident, not a natural-born citizen, and Section 3 of the 14th Amendment is one of those qualifications," she said, noting that if a political party wanted to list former California Gov. Arnold Schwarzenegger on the Colorado ballot, for example, her office would not allow it because he is not a natural-born citizen.

Trump's actions, Griswold argued, are those of an "insurrectionist," and the Constitution has a "clear answer to what follows: that person is ineligible from holding office again."

"The presidency should not be a get-out-of-jail card, and the American people deserve leaders who are qualified to serve in the offices they are running for," she said.

What happens if the Supreme Court rules in Trump's favor?

The case has divided legal scholars, though many agree it's imperative for the Supreme Court to settle the disqualification dispute on the merits.

Voters in 15 states, including Colorado, are set to cast their ballots for the Republican primary on March 5, Super Tuesday. Courts in Maine and Oregon have cited the pending case before the Supreme Court in turning away challenges to Trump's eligibility.

"The idea that you have somebody out there who is, in the view of courts, secretaries of state, whomever, ineligible to run, that needs to be decided," Millen said. "We need to know that we've got eligible candidates going into the general election."

A victory for Trump could come in several forms. A majority of the justices could find that Section 3 does not apply to the president or office of the presidency. It could determine that Trump did not engage in any event that qualifies as "insurrection," or conclude that only Congress can enforce Section 3. Five justices could also rule that the Colorado Supreme Court did not have the authority under state election law to order Trump removed from the ballot.

If the Supreme Court rules in favor of Trump on any one of those issues, he would remain on the primary and general election ballots for the 2024 presidential race.

But if a majority of the justices side with the voters and uphold the Colorado Supreme Court's decision, which many scholars believe is unlikely, he could be barred from holding the presidency, leading states to remove him from their ballots.

"This is what the Constitution commands. Donald Trump engaged in insurrection and is disqualified from holding office again," Olson said. "The process in Colorado demonstrating Trump's engagement in that insurrection, how he incited the mob, called them to Washington before that, was overwhelming, and I think a failure to recognize those facts or escape on a legal technicality would do great disservice to the rule of law in our country."

Referring to a friend-of-the-court brief filed by a group of six experts on democracy, political violence and the rule of law, Olson said, "the only way to preserve our democracy is to uphold our Constitution, and when we shrink away from that bedrock commitment, we threaten the stability and ongoing vitality of our country."

Melissa Quinn

Melissa Quinn is a politics reporter for CBSNews.com. She has written for outlets including the Washington Examiner, Daily Signal and Alexandria Times. Melissa covers U.S. politics, with a focus on the Supreme Court and federal courts.

Twitter