Discussion of a relatively obscure clause in the U.S. Constitution that would disqualify certain individuals from holding office began shortly after the Jan. 6, 2021, attack at the U.S. Capitol.
It began among law professors and lawyers who had been looking at Section 3 of the 14th Amendment, which was ratified into the Constitution after the Civil War to keep former Confederates out of federal and state government.
The clause was reintroduced into the legal debate during the 2022 midterm elections, when government watchdog groups mounted serious challenges to elected officeholders -- efforts that some lawyers have called a "test run" for applying the legal theory to former President Donald Trump.
The theory behind the ban has recently been used by secretaries of state, considered by lower level state judicial systems and even accepted by leading conservative law scholars. In December, Section 3 was finally applied to Trump in Colorado, where the top court disqualified him from running on the state's GOP presidential primary ballot.
MORE: Should Justice Thomas recuse in Trump 14th Amendment case because of wife's Jan. 6 role?The use of Section 3 has now hit a fever pitch, with the nation's highest court considering a blockbuster case involving Trump's ballot eligibility under the clause.
The possibility that this clause could disqualify a candidate, let alone a front-runner, has been met with widespread skepticism. Many legal scholars maintain that the U.S. Supreme Court will demur under the very high bar it sets to take someone off a ballot. But others have maintained that the legal theory can withstand scrutiny.
"A lot of people said this was a long shot case," said Noah Bookbinder, the president of the watchdog group Citizens for Responsibility and Ethics in Washington (CREW), which filed the Colorado case with six voters."But legally and factually, this is a very strong case."
The Section 3 question has faced a number of key inflection points over the past three years as it wound its way to the Supreme Court.
Josh Blackman is one of two conservative law professors who authored the widely cited paper that popularized the argument that Section 3's reference to "an officer of the United States" does not include the president -- a theory at the center of Trump's argument before the Supreme Court.
He and his co-author, Seth Barrett Tillman, have explored the argument since 2008. On Jan. 6, 2021, the scholar said that he connected with Tillman and began writing -- on the First Amendment, Trump's Jan. 6 speech, and then Section 3.
Blackman, who wrote an amicus brief on behalf of Trump ahead of the Colorado Supreme Court hearing and another ahead of Thursday's U.S. Supreme Court arguments, said he anticipated that Section 3 might be applied following the Capitol riots, but just didn't know when.
"I didn't know when it would happen -- the primary or the general election and which state it would be in," he told ABC News.
MORE: Experts dissect key arguments in Colorado Supreme Court 14th Amendment ruling"But the target's too attractive -- that the way to knock out the leading candidate of a political party is the courts, not the ballot box. it was just because it was too attractive of a target. It was not not going to happen. And I knew as soon as any court knocked him off the ballot the U.S. Supreme Court would have to take it," Blackman said.
Mark Graber, a constitutional scholar and law professor at the University of Maryland, had also been studying the framing of Section 3 for almost a decade.
He said that he wasn't surprised that the clause in its application to Trump had made its way to the Supreme Court, and that the Colorado decision had really exposed the strength of some of the challengers' arguments.
"Before, before Colorado, people weren't really engaged with the argument. They were sort of saying it's never gonna work. Once people started to look at the arguments, they realized the arguments for this disqualification are quite strong," he said.
Several disqualification clause cases in 2022 -- against Rep. Marjorie Taylor Greene of Georgia and former-Rep. Madison Cawthorn of North Carolina, and Arizona Reps. Paul Gosar and Andy Biggs due to their alleged support for the Jan. 6 attack on the Capitol -- were tossed out.
But one public official, former Otero County, New Mexico, Commissioner Couy Griffin, was disqualified in 2022 after CREW sued to eject him from his role under Section 3.
Griffin's case was a bench trial decided by a state judge and he has since twice appealed to the New Mexico Supreme Court with no success. Griffin was convicted of trespassing at the U.S. Capitol two years ago, though he said he did not enter the building with the mob. He was found not guilty of disorderly conduct.
MORE: Official removed from office under 14th Amendment speaks out as Trump case loomsIt was after Griffin's disqualification that some constitutional experts suggested that section of the law could have wide-ranging implications, especially for Trump if he ran again for the White House.
"Just the fact that this has happened one time, if it stands up on appeal, makes the future challenges more credible than if no one had ever been disqualified for their participation in January 6 … Up until now it seemed like more of a hypothetical," Gerard Magliocca, a constitutional scholar at Indiana University who is one of the paramount experts on the clause, told ABC News in 2022. He later testified during the Colorado evidentiary hearing.
"If Griffin is disqualified, then it's a little hard to see why Trump wouldn't be disqualified," Magliocca added.
Others, like conservative lawyer James Bopp Jr., who represented Greene and Cawthorn, said the "test run" cases were simply political stunts that wouldn't carry much weight.
"I've never felt that there was any legal basis for these challenges," Bopp Jr. said to ABC News.
"You can get traction particularly in the context in which this is highly politically charged and ideologically charged. And the reality is we have some very left wing judges and left wing state officials that could be expected to entertain this idea," he added.
In August, a growing body of conservative scholars raised the constitutional argument that Trump's efforts to overturn the results of the 2020 election make him ineligible to hold federal office ever again.
Two members of the conservative Federalist Society, William Baude and Michael Stokes Paulsen, endorsed the disqualification clause in the pages of the Pennsylvania Law Review.
Then, two more legal scholars -- retired conservative federal appeals court judge J. Michael Luttig and Harvard Law Professor Emeritus Laurence Tribe -- made the same case in an article published in The Atlantic.
Many consider this to be sort of a turning point in the provision's lifecycle.
"What Baude and Paulson did was made clear this was not simply a lot of lefties. They made clear that for many others, Donald Trump was not qualified to be president," said Graber.
Blackman agreed: "[The scholars] bent the arc of history. If it wasn't for the article, I don't think the Colorado court would have ruled the way it did," he said.
About a month later, the legal theory further gained steam, with election officials in key states preparing for or starting to respond to legal challenges to Trump's candidacy.
In September, lawsuits were filed in Colorado by CREW and in Minnesota by Free Speech For People (FSFP), the watchdog group who led Greene and Cawthorn's challenges. Another FSFP suit followed shortly after in Michigan, but the two midwestern challenges were ultimately rejected.
The Colorado case was assigned a evidentiary hearing in Colorado District Court. Over five days, experts like Magliocca testified, along with witnesses including two police officers who were at the Capitol on Jan. 6 and California Rep. Eric Swalwell, who was inside the chamber and retiring Rep. Ken Buck of Colorado.
In November, state District Judge Sarah B. Wallace ruled that Trump could remain on Colorado's GOP ballot, but stunningly wrote that he had "engaged in insurrection" on Jan. 6. The decision was quickly appealed to the Colorado Supreme Court, who ordered in a 4-3 decision that Trump had engaged in insurrection and was thus disqualified under Section 3 -- a ruling that was quickly appealed by the former president's team and was taken up by the Supreme Court.
Now, the Supreme Court could have the final say in on the clause as it pertains to Trump, or how it applies to the U.S. presidency in the future.