The other, more politically perilous option would be for one or more states to embrace the theory outright and simply refuse to list Trump on their ballots. That might force Trump to file his own lawsuits asking courts to order his candidacy restored in those states. So far, no state has moved to bar Trump from the ballot, though secretaries of state around the nation are discussing the issue among themselves.

Either scenario could thrust the courts, and likely the Supreme Court, into an unsettled debate over the meaning of the insurrection clause, a long-winded 110-word provision that was ratified in 1868 and has rarely been interpreted — or even invoked — since then.

Here’s what you need to know about the 14th Amendment theory.

What is the insurrection clause?

In short, the clause says anyone who “engaged in insurrection or rebellion” after taking an oath of office to defend the Constitution is forbidden from holding any public office. When the 14th Amendment was drafted after the Civil War, the clause was aimed at preventing Southern states from electing former Confederate officers to Congress.

The text in question is from section three of the amendment, and it says the following:

“No person shall be a Senator or Representative in Congress, or elector of President and Vice President, or hold any office, civil or military, under the United States, or under any State, who, having previously taken an 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, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof. But Congress may, by a vote of two-thirds of each House, remove such disability.”

According to the legal scholars arguing the provision applies to Trump, the disqualification is “self-executing,” meaning it automatically applies to whomever meets the criteria described in the amendment and doesn’t require another element — say, a criminal conviction tied to the insurrection — to trigger it. The only way around the disqualification is for Congress to grant amnesty by a two-thirds vote in each chamber.

Who has endorsed the theory?

Several prominent constitutional scholars have said in recent weeks that they believe the 14th Amendment renders Trump ineligible to take office as president again.

William Baude and Michael Stokes Paulsen, two conservative law professors, wrote an article that is set to be published in the University of Pennsylvania Law Review next year. They argue that the provision is intended to “embrace a broad range of willful participatory conduct” as qualifying for having “engaged in” insurrection or rebellion. And they say Trump’s actions — particularly his efforts to pressure then-Vice President Mike Pence to prevent the counting of electoral votes and Trump’s “incendiary” speech encouraging supporters to march to the Capitol on Jan. 6 — clearly meet the standard.

J. Michael Luttig, a conservative former federal judge, and Laurence Tribe, a liberal constitutional law professor, agree. “The former president’s efforts to overturn the 2020 presidential election, and the resulting attack on the U.S. Capitol, place him squarely within the ambit of the disqualification clause, and he is therefore ineligible to serve as president ever again,” they wrote in the Atlantic last month.

What is the counter-argument?

Not all legal scholars agree with these interpretations of section three of the 14th Amendment. Skeptics say the recent interpretations embrace overly broad definitions of the amendment’s language, and they argue that the criminal-justice system is the appropriate enforcement mechanism for preventing someone who participated in an insurrection from holding office.

Stanford Law School professor Michael McConnell, for example, cautioned against “too loose” an interpretation of the provision, suggesting the terms “insurrection” or “rebellion” should apply to “only the most serious of uprisings against the government,” such as the Civil War.

Others have also expressed concern about the precedent of secretaries of state unilaterally disqualifying certain politicians from the ballot, suggesting such a step might be seen as undemocratic. And there are possible political implications to removing Trump, with such an act likely to prompt a backlash from his supporters.

How would the 14th Amendment theory be put into practice?

Most likely it would need to be enforced as the result of a lawsuit. A candidate running against Trump in either the Republican primary or the general election would have the cleanest path into court, because they could argue that they are directly harmed by Trump’s presence on the ballot. Interest groups or individual voters also could try to sue to prevent him from getting on the ballot in a particular state.

In recent days, a longshot Republican presidential candidate, John Anthony Castro, filed a lawsuit in New Hampshire arguing that Trump violated the 14th Amendment and seeking an injunction that would force the state’s secretary of state to keep Trump’s name off the ballot. And in Florida, a tax attorney sued Trump in federal court in an effort to disqualify him from running for president, saying his participation in the events of Jan. 6 should prevent him from holding office under the 14th Amendment.

Alternatively, a secretary of state could preemptively exclude him from the ballot, almost certainly leading Trump to sue over it. Some secretaries of state have already suggested they will at least consider whether to apply the provision. Michigan Secretary of State Jocelyn Benson said she planned to speak with her counterparts in other battleground states about how to handle the issue.

Over the summer, legal advocacy group Free Speech for People sent letters to secretaries of state and chief election officials in nine states asking them to bar Trump from the ballot as a consequence of the 14th Amendment. “Trump’s involvement in the violent attack on Congress to prevent the certification of democratic election results disqualifies him from holding any future public office,” they wrote.

Either way, the issue is likely to result in multiple appeals from Trump and his campaign or from a conservative group. Any serious effort to ban him from the ballot likely would rocket up to the Supreme Court.

It has already become a point of dispute in New Hampshire. Bryant “Corky” Messner, an attorney who ran on Trump’s endorsement as Republicans’ 2020 U.S. Senate nominee, questioned Trump’s eligibility for the ballot and met with New Hampshire’s secretary of state, David Scanlan, asking him to seek legal guidance on the issue. Scanlan and New Hampshire’s attorney general, John Formella — both of whom are Republicans — then issued a joint statement saying Formella’s office “is now carefully reviewing the legal issues involved.”

The chair of the state’s Republican Party, however, said the group would “fight to make sure that candidates are not denied access to the ballot.”

How has the 14th Amendment theory fared in the courts?

In the century and a half since the 14th Amendment was ratified, its third section has been infrequently tested in court, and never against a former president.

After Jan. 6, Free Speech for People filed legal challenges against Republican Rep. Marjorie Taylor Greene (R-Ga.) and then-Rep. Madison Cawthorn (R-N.C.), arguing that both were ineligible for office under the insurrection clause. In Greene’s case, an administrative law judge found that she didn’t participate in the Jan. 6 insurrection, making her eligible to run for reelection.

In Cawthorn’s case, a federal appeals court ruled against him, but the ruling came after he had already lost his primary.