Donald J. Trump’s eligibility for the presidential ballot has been challenged in more than 30 states, but only a handful of those cases have gained traction so far.John Anthony Castro, a 40-year-old Texan, long-shot Republican presidential candidate and the most prolific challenger of Donald J. Trump’s eligibility to be president, has gone to court in at least 27 states trying to remove the former president from the ballot.On Wednesday, Mr. Castro found himself in a mostly empty courthouse in New Hampshire’s capital, where he was making a second attempt to advance his arguments; his initial case was dismissed last fall.None of Mr. Castro’s lawsuits have succeeded. But the New Hampshire case is part of a growing constellation of ballot challenges — some lodged by established groups with national reach, many others far more homemade — that have been playing out in more than 30 states. Challengers in Colorado and Maine have succeeded, at least temporarily, in getting Mr. Trump disqualified, while other lawsuits have stalled or been dismissed. In at least 22 states, cases have yet to be resolved.Tracking Efforts to Remove Trump From the 2024 BallotSee which states have challenges seeking to bar Donald J. Trump from the presidential primary ballot.All the litigation has made for an odd, diffuse process in which some of the weightiest issues of American democracy are being raised not primarily by elected officials or a political party, but by an unlikely assortment of obscure figures, everyday citizens and nonprofit groups. Even some of the players are wondering what they are doing there.“How did we get to this point, where you have random brewers in Wisconsin throwing Hail Marys to try to get Trump off the ballot?” said Kirk Bangstad, a brewing company owner and liberal activist who filed an unsuccessful challenge to Mr. Trump’s eligibility with the Wisconsin Elections Commission. Mr. Bangstad, who is now considering a lawsuit, readily admits that he wishes someone more prominent would have taken up the cause.Kirk Bangstad, a brewing company owner and liberal activist who filed an unsuccessful challenge of Mr. Trump’s eligibility with the Wisconsin Elections Commission.Chang W. Lee/The New York TimesThough the ballot challenges vary in format, venue and sophistication, they share a focus on whether Mr. Trump’s efforts to overturn his 2020 election defeat make him ineligible to hold the presidency again. The cases are based on a largely untested clause of the Constitution’s 14th Amendment, which was enacted after the Civil War. The clause bars federal or state officials who “engaged in insurrection or rebellion” from holding office.Some lawyers have argued since 2021 that the clause could preclude Mr. Trump from appearing on a presidential ballot, and lawsuits invoking that theory were filed in several states in 2023. But it was not until last month, when the Colorado Supreme Court found Mr. Trump ineligible for that state’s primary ballot because of the 14th Amendment, that the question vaulted to the center of American politics. When Maine’s Democratic secretary of state announced last week that she, too, was disqualifying Mr. Trump, it only intensified the spotlight on the issue.Steven Cheung, a spokesman for the Trump campaign, described the lawsuits in a statement last week as “bad-faith, politically motivated attempts to steal the 2024 election,” claiming that Democrats had “launched a multifront lawfare campaign to disenfranchise tens of millions of American voters and interfere in the election.” Mr. Cheung did not respond to a request for comment for this article.Mr. Trump filed a lawsuit in state court in Maine on Tuesday seeking to overturn the secretary of state’s decision, and on Wednesday he asked the U.S. Supreme Court to review the Colorado ruling.The issue could not be more urgent: Republican presidential primary elections and caucuses begin this month, and polls have shown Mr. Trump with a commanding lead over his opponents.In the meantime, other cases continue to wind their way through state and federal court systems.Those lawsuits can generally be divided into three categories: Mr. Castro’s lawsuits, almost all of which have been filed in federal court; state challenges filed by two nonprofit organizations; and one-off cases brought in state or federal courts by local residents. In a handful of places — most notably Maine, but also Illinois, Massachusetts, North Carolina and Wisconsin — voters have challenged Mr. Trump’s eligibility directly with a secretary of state or an election commission rather than in court. In California and New York, some elected officials have written letters pushing for elections officers in those states to disqualify or consider disqualifying the former president.Most establishment Democrats have not publicly embraced the cause. President Biden said after the Colorado Supreme Court ruling that it was “self-evident” that Mr. Trump had supported an insurrection, but that it was up to the judiciary to determine his eligibility for the ballot. Several Democratic secretaries of state, who in much of the country are their states’ chief election officers, have included Mr. Trump on candidate lists and deferred to the courts on the question of his eligibility. A growing constellation of challenges to Mr. Trump’s eligibility have been filed in courts across the country, including federal court in Concord, N.H.Neville Caulfield for The New York TimesThe two national groups are Citizens for Responsibility and Ethics in Washington, known as CREW, which brought the Colorado case, and Free Speech for People, which filed lawsuits in Michigan, Minnesota and Oregon, as well as complaints with election officials in Illinois and Massachusetts. Those two groups have focused on state-level challenges. The Michigan and Minnesota Supreme Courts declined to take Mr. Trump off the primary ballot in those states. The Oregon lawsuit is still pending, as are the objections in Illinois and Massachusetts, which were both filed on Thursday.Ben Clements, the chairman of Free Speech for People, said he believed challenges originating in federal court “are not helpful” to the disqualification cause because of concerns about plaintiffs not having the legal standing to bring a case. But he said the array of lawsuits in state courts — such challenges were pending this week in California, Florida, Louisiana, North Carolina, Oregon, Wisconsin and Wyoming — were welcome.“Even if we wanted to, and even if CREW had taken an approach of filing multiple suits, we’re not going to hit all 50 states,” Mr. Clements said.Many people expect the U.S. Supreme Court to ultimately decide the question of Mr. Trump’s eligibility. And outside of a few states, the challenges so far have not gained traction.Some cases have been dismissed, including a federal lawsuit in Virginia and Mr. Bangstad’s complaint in Wisconsin, both last week. Others have been withdrawn, including several of Mr. Castro’s lawsuits and a state case in New Jersey filed by John Bellocchio, a former history teacher. In an interview, Mr. Bellocchio said he was working on a second lawsuit, and that he was motivated by concern that the former president and his supporters “envision a Christian theocracy.”“You cannot have a theocracy and a democracy at the same time,” Mr. Bellocchio said in an interview.By far, the most persistent litigant is Mr. Castro, who, according to his campaign website, first ran for a county office at the age of 19 and has since run unsuccessfully at least twice for other offices, including in a special congressional election in 2021.Mr. Castro received a law degree from the University of New Mexico and a master’s degree from Georgetown’s law school. He said he had never been licensed as a lawyer by any state, but was certified by the I.R.S. to work on federal tax cases. Over the years, he has been involved in a dizzying array of legal disputes.Mr. Castro said he had hoped that someone better known would mount a Republican presidential campaign to challenge Mr. Trump’s ballot qualifications, but when no one else stepped up, he decided to do it himself.“My biggest fear was having the knowledge how to stop Trump and having to tell my grandchildren that I did nothing,” he said.At Wednesday’s federal court hearing, Mr. Castro needed to persuade Judge Samantha Elliott that he was a real candidate for the Republican nomination for president and had the legal standing to sue.Among his evidence: He had filed reports with the Federal Election Commission (as of September, records show his campaign had raised $678), and two of his relatives had driven around New Hampshire one day in October, installing a dozen yard signs, before flying home to Texas.In the courtroom on Wednesday, Mr. Castro appeared at times to be unfamiliar with court procedures. But he seemed to come to life as he cross-examined Michael Dennehy, a veteran political strategist and expert witness for Mr. Trump, who testified that it would be “impossible” for Mr. Castro to win any delegates in the state based on his nearly “nonexistent” fund-raising and campaign.If Mr. Castro’s goal is to disqualify Mr. Trump, some observers have suggested that his strategy may backfire.Derek Muller, an election law expert and professor at Notre Dame’s law school, said Mr. Castro risked creating unfavorable precedent with his failed lawsuits. Mr. Trump has already been able to use a judge’s opinion in one state — in which the judge dismissed a Castro lawsuit — to bolster his arguments in another.Mr. Castro is “single-handedly building up precedent for Trump, inadvertently,” said Mr. Muller, who has filed briefs in two state court cases analyzing the relevant election law.Mr. Castro disagreed. If anything, he said, his suits have forced Mr. Trump’s lawyers to “show their cards,” helping other challengers to hone their arguments. He said he plans to refile lawsuits in three more states this month.Tracey Tully More