Is Trump Disqualified? Republicans Prepare to Fight Long-Shot Legal Theory.

New Hampshire’s first-in-the-nation primary is quickly becoming the leading edge for an unproven legal theory that Donald J. Trump is disqualified from appearing on the ballot under the 14th Amendment of the U.S. Constitution.

A long-shot presidential candidate has filed a lawsuit in state court seeking an injunction to keep Mr. Trump off the ballot. And a former Republican candidate for Senate is urging the secretary of state to bring a case that could put the issue before the U.S. Supreme Court.

On Wednesday, Free Speech for the People, a liberal-leaning group that unsuccessfully tried to strike House Republicans from the ballot in 2022, sent a letter to the secretaries of state in New Hampshire, as well as Florida, New Mexico, Ohio and Wisconsin, urging them to bar Mr. Trump from the ballot under the 14th Amendment.

These efforts employ a theory that has been gaining traction among liberals and anti-Trump conservatives: that Mr. Trump’s actions on Jan. 6, 2021, disqualify him under Section 3 of the 14th Amendment, which bars people from holding office if they took an oath to support the Constitution and later “engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof.”

The theory has been gaining momentum since two prominent conservative law professors published an article this month concluding that Mr. Trump is constitutionally disqualified from running for office.

But even advocates of the disqualification theory say it is a legal long shot. If a secretary of state strikes Mr. Trump’s name or a voter lawsuit advances, Mr. Trump’s campaign is sure to appeal, possibly all the way to the Supreme Court, where the 6-3 conservative majority includes three justices nominated by Mr. Trump.

“When it gets to the Supreme Court, as it surely will, this will test the dedication of the justices to principles of law, more than almost anything has for a very long time,” said Laurence H. Tribe, a constitutional law professor at Harvard who believes the insurrection disqualification clearly applies to Mr. Trump, “because they will obviously realize that telling the leading candidate of one major political party, ‘no, no way, you’re not eligible’ is no small matter.”

However long the odds of success, discussion of the amendment is bubbling up across the country. In Arizona, the secretary of state said he had heard from “concerned citizens” about the issue, and the Michigan secretary of state said she was “taking it seriously.” In Georgia, officials are looking at precedent set by a failed attempt to use the 14th Amendment to disqualify Representative Marjorie Taylor Greene from the ballot in the 2022 midterms.

But New Hampshire has jumped out as the early hotbed of the fight.

The New Hampshire Republican Party said this week that it would challenge any effort to remove Mr. Trump, or any other candidates who have met requirements, from the ballot.

“There’s no question that we will fight, and we’ll use all of the tools available to us to fight anyone’s access being denied on the ballot,” said Chris Ager, a Republican state committeeman in New Hampshire. “And if there’s a lawsuit, we are likely to intervene on behalf of the candidate to make sure that they have access. So we take it very seriously that the people of New Hampshire should decide who the nominee is, not a judge, not a justice system.”

Late last week, Bryant Messner, a former Trump-endorsed candidate for U.S. Senate, who goes by Corky, met with New Hampshire’s secretary of state, David M. Scanlan, to urge him to seek legal guidance on the issue. After Politico first reported the meeting, Mr. Scanlan and John M. Formella, the state’s attorney general, issued a joint statement saying that “the attorney general’s office is now carefully reviewing the legal issues involved.”

Other secretaries of state have also been seeking legal guidance.

“We’re taking a very cautious approach to the issue,” Arizona’s secretary of state, Adrian Fontes, said in an interview. “We’re going to be consulting with lawyers in our office and other folks who will eventually have to deal with this in the courts as well. We don’t anticipate that any decision that I or any other election administrator might make will be the final decision. This will get ultimately decided by the courts.”

Though the argument is particularly appealing to liberals who view Mr. Trump as a grave threat, most of the recent momentum on this topic has come from conservative circles.

Mr. Messner, a self-described “constitutional conservative,” said he was seeking to create case law around the issue. He said he had not yet filed a legal challenge because he first wanted the secretary of state to open up the candidate filing period and decide whether he would accept Mr. Trump’s filing. He argued that the lawsuit filed on Sunday by a Republican candidate, John Anthony Castro, was unlikely to advance because the filing period has not yet opened.

“Section 3 has not been interpreted,” Mr. Messner said in an interview. “So, my position is let’s find a way for this to get into the court system as soon as possible. And then hopefully we can expedite through the legal system, to get it to the Supreme Court as soon as possible.”

The precedent is by no means settled. A case filed against then-Representative Madison Cawthorn, Republican of North Carolina, ended with Judge Richard E. Myers II of U.S. District Court, an appointee of Mr. Trump, siding with Mr. Cawthorn. The judge ruled that the final clause of Section 3 allowed for a vote in Congress to “remove” the disqualification and that the passage of the Amnesty Act of 1872 effectively nullified the ban on insurrectionists.

But on appeal, the U.S. Court of Appeals of the Fourth Circuit overruled that argument, saying the Amnesty Act clearly applied only to confederates, not future insurrectionists. The case was declared moot after Mr. Cawthorn lost his re-election in the 2022 primaries.

Other cases may also come into play. An administrative law judge in Georgia ruled that plaintiffs failed to prove that Representative Marjorie Taylor Greene, Republican of Georgia, was in fact an insurrectionist. And cases against Representatives Paul Gosar and Andy Biggs, Republicans of Arizona, were similarly dropped.

Advocates of the disqualification clause fear that judges and secretaries of state could decide that any case against Mr. Trump will have to wait until a jury, either in Fulton County, Ga., or Washington, D.C., renders judgment in the two criminal cases charging that Mr. Trump had tried to overturn the 2020 election.

Secretary of State Brad Raffensperger of Georgia indicated that previous cases involving Ms. Greene would continue to guide his office, and that “as secretary of state of Georgia, I have been clear that I believe voters are smart and deserve the right to decide elections.”

“In Georgia, there is a specific statutory process to follow when a candidate’s qualifications for office are challenged,” Mr. Raffensperger said in a statement. “The secretary of state’s office has and will continue to follow the appropriate procedures in state law for any candidate challenges.”

There has been one settled case since Jan. 6 that invoked the 14th Amendment. In September, a judge in New Mexico ordered a county commissioner convicted of participating in the Jan. 6 riot removed from office under the 14th Amendment. He was the first public official in more than a century to be barred from serving under a constitutional ban on insurrectionists holding office.