On a late January afternoon, two senior prosecutors stood before the new Manhattan district attorney, hoping to persuade him to criminally charge the former president of the United States.The prosecutors, Mark F. Pomerantz and Carey R. Dunne, detailed their strategy for proving that Donald J. Trump knew his annual financial statements were works of fiction. Time was running out: The grand jury hearing evidence against Mr. Trump was set to expire in the spring. They needed the district attorney, Alvin Bragg, to decide whether to seek charges.But Mr. Bragg and his senior aides, masked and gathered around a conference table on the eighth floor of the district attorney’s office in Lower Manhattan, had serious doubts. They hammered Mr. Pomerantz and Mr. Dunne about whether they could show that Mr. Trump had intended to break the law by inflating the value of his assets in the annual statements, a necessary element to prove the case.The questioning was so intense that as the meeting ended, Mr. Dunne, exasperated, used a lawyerly expression that normally refers to a judge’s fiery questioning:“Wow, this was a really hot bench,” Mr. Dunne said, according to people with knowledge of the meeting. “What I’m hearing is you have great concerns.”The meeting, on Jan. 24, started a series of events that brought the investigation of Mr. Trump to a sudden halt, and late last month prompted Mr. Pomerantz and Mr. Dunne to resign. It also represented a drastic shift: Mr. Bragg’s predecessor, Cyrus R. Vance Jr., had deliberated for months before deciding to move toward an indictment of Mr. Trump. Mr. Bragg, not two months into his tenure, reversed that decision.Mr. Bragg has maintained that the three-year inquiry is continuing. But the reversal, for now, has eliminated one of the gravest legal threats facing the former president.This account of the investigation’s unraveling, drawn from interviews with more than a dozen people knowledgeable about the events, pulls back a curtain on one of the most consequential prosecutorial decisions in U.S. history. Had the district attorney’s office secured an indictment, Mr. Trump would have been the first current or former president to be criminally charged.Mr. Bragg was not the only one to question the strength of the case, the interviews show. Late last year, three career prosecutors in the district attorney’s office opted to leave the investigation, uncomfortable with the speed at which it was proceeding and with what they maintained were gaps in the evidence. The tension spilled into the new administration, with some career prosecutors raising concerns directly to the new district attorney’s team.Mr. Bragg, whose office is conducting the investigation along with lawyers working for New York’s attorney general, Letitia James, had not taken issue with Mr. Dunne and Mr. Pomerantz presenting evidence to the grand jury in his first days as district attorney. But as the weeks passed, he developed concerns about the challenge of showing Mr. Trump’s intent — a requirement for proving that he criminally falsified his business records — and about the risks of relying on the former president’s onetime fixer, Michael D. Cohen, as a key witness.Mr. Cohen’s testimony, the prosecutors leading the investigation argued, could help to establish that Mr. Trump was intentionally misleading when he exaggerated the value of his properties. The financial statements Mr. Trump submitted to banks to secure loans — documents that say “Donald J. Trump is responsible for the preparation and fair presentation” of the valuations — could also support a case.Mr. Bragg was not persuaded. Once he told Mr. Pomerantz and Mr. Dunne that he was not prepared to authorize charges, they resigned. Explaining the resignation to his team of prosecutors in a meeting a day later, Mr. Dunne said he felt he needed “to disassociate myself with this decision because I think it was on the wrong side of history.”Mr. Dunne and Mr. Pomerantz also bristled at how Mr. Bragg had handled the investigation at times. Mr. Bragg left the pivotal Jan. 24 meeting before the discussion ended, though several of his top aides stayed behind. And after that day, Mr. Dunne and Mr. Pomerantz — two of New York’s most prominent litigators, who had become accustomed to driving the case — were not included in closed-door meetings where decisions were made.Mark Pomerantz, one of two lawyers who were leading a criminal inquiry into former President Donald J. Trump’s business practices. The two resigned last week after the investigation came to a sudden halt.David Karp/Associated PressMr. Bragg’s choice not to pursue charges is reminiscent of the high hurdle that others have failed to clear over the years as they sought to hold Mr. Trump criminally liable for his practices as a real estate mogul. Mr. Trump famously shuns email, and he has cultivated deep loyalty among employees who might otherwise testify against him, a one-two punch that has stymied other prosecutors in search of conclusive proof of his guilt.In the Manhattan investigation, the absence of damning emails or an insider willing to testify would make it harder to prove that any exaggerations were criminal. Mr. Trump, who has a history of making false statements, has in the past referred to boastful claims about his assets as “truthful hyperbole.”The interviews with people knowledgeable about the Manhattan investigation also highlight the success of Mr. Trump’s efforts to delay it.He fought many of the subpoenas issued by the district attorney. In one of those battles — for Mr. Trump’s tax returns and other financial documents — it took nearly 18 months and two trips to the Supreme Court for Mr. Vance’s office to obtain the records. As a result, the ultimate decision of whether to pursue charges fell to Mr. Bragg, his more skeptical successor.A public uproar over his handling of the investigation has added to the turbulence of Mr. Bragg’s early tenure.As he was weighing the fate of the Trump investigation, Mr. Bragg was also contending with a firestorm over a number of criminal justice reforms he introduced in a memo his first week in office. The memo immediately embroiled his administration in controversy, a public relations debacle that worsened with a handful of high-profile shootings, including the killing of two police officers in late January.Although it is unclear whether those early travails influenced Mr. Bragg’s management of the Trump inquiry, there is no doubt that they contributed to his frenzied first days in office.Mr. Bragg’s decision on the Trump investigation may compound his political problems in heavily Democratic Manhattan, where many residents make no secret of their enmity for Mr. Trump.Mr. Bragg has told aides that the inquiry could move forward if a new piece of evidence is unearthed, or if a Trump Organization insider decides to turn on Mr. Trump. Other prosecutors in the office saw that as fanciful.Mr. Trump has long denied wrongdoing and has accused Mr. Bragg and Ms. James, both of whom are Democrats and Black, of carrying out a politically motivated “witch hunt” and being “racists.”Danielle Filson, a spokeswoman for Mr. Bragg, said that the investigation into Mr. Trump was continuing under new leadership.“This is an active investigation and there is a strong team in place working on it,” Ms. Filson said. She added that the inquiry was now being led by Susan Hoffinger, the executive assistant district attorney in charge of the office’s Investigation Division.Mr. Pomerantz and Mr. Dunne declined to comment.The Brain TrustCyrus R. Vance Jr., the previous Manhattan district attorney, began the investigation into Mr. Trump, including whether he had intentionally inflated the value of his assets to defraud lenders.Desiree Rios for The New York TimesMr. Vance and his top deputies were riding high last summer.They had just announced criminal tax charges against Mr. Trump’s family business and his longtime finance chief, Allen H. Weisselberg. The next step for Mr. Dunne, Mr. Pomerantz and their team was to build a case against Mr. Trump himself.The two were suited to the task. Mr. Pomerantz, 70, had once run the criminal division of the U.S. attorney’s office in Manhattan. He had also been a partner at the prestigious law firm Paul Weiss, and he came out of retirement to work on the investigation without pay.Mr. Dunne had begun his career trying cases as an assistant district attorney in Manhattan, gone on to become a partner at another top firm, Davis Polk, and was a former president of the New York City bar association. As Mr. Vance’s general counsel, he had successfully argued before the Supreme Court, winning access to Mr. Trump’s tax records.Helped by lawyers from Ms. James’s office, which was conducting a separate, civil inquiry into Mr. Trump, Mr. Dunne and Mr. Pomerantz pressed ahead with their investigation into whether Mr. Trump had used his financial statements to deceive lenders about his net worth and secure favorable loan terms. Mr. Cohen had testified before Congress that Mr. Trump was a “con man” who “inflated his total assets when it served his purposes.”By the fall, a number of the prosecutors assigned to the investigation thought it was likely that Mr. Trump had broken the law. Proving it would be another matter.Letitia James, New York’s attorney general, has been leading a parallel inquiry focused on whether financial statements for Mr. Trump’s family company intentionally included false information.Todd Heisler/The New York TimesSoon, some of the career prosecutors who had worked on the inquiry for more than two years expressed concern. They believed that Mr. Vance, who had decided not to seek re-election, was pushing too hard for an indictment before leaving office, and that the evidence gathered so far did not justify the speed at which the inquiry was moving.The debate was born of painful experience from past investigations, including one involving the Trump family. In 2012, in the first of his three terms, Mr. Vance closed an investigation into accusations that Mr. Trump’s son Donald Jr. and his daughter Ivanka had misled potential buyers of apartments at one of the Trump Organization’s New York hotels, Trump Soho. The decision trailed Mr. Vance for years, subjecting him to criticism after Mr. Trump was elected president.Concern among the office’s career prosecutors about the investigation into the former president came to a head in September at a meeting they sought with Mr. Dunne. Mr. Dunne offered to have them work only on the pending trial of Mr. Weisselberg or leave the Trump team altogether.Two prosecutors eventually took him up on the latter.Mr. Vance pressed on, and in early November, convened a new special grand jury to start hearing evidence against the former president. Still, he had yet to decide whether to direct the prosecutors to begin a formal grand jury presentation with the goal of seeking charges. As his tenure drew to a close in December, he consulted a group of prominent outside lawyers to help inform what would be his final decision.The group was referred to internally as “the brain trust” — a handful of former prosecutors that included two senior members of Robert S. Mueller’s special counsel inquiry into Mr. Trump’s 2016 campaign.Before they all convened for a meeting on Dec. 9, Mr. Dunne and Mr. Pomerantz circulated hypothetical opening arguments in advance: one for the prosecution; another for the defense.In the meeting, which lasted much of the day, the outside lawyers raised a number of questions about the evidence and the lack of an insider witness. Mr. Weisselberg, who has spent nearly a half-century working as an accountant for the Trump family, had resisted pressure from the prosecutors to cooperate.The brain trust puzzled over how to prove that Mr. Trump had intended to commit crimes, and the group questioned Mr. Cohen’s potential strength as a witness at trial. A former Trump acolyte turned antagonist, Mr. Cohen pleaded guilty in 2018 to federal charges of lying to Congress on behalf of Mr. Trump and paying hush money to a pornographic actress who said she had an affair with Mr. Trump.Mr. Bragg, who had not yet been sworn in, was not aware of the Dec. 9 meeting.And there are differing accounts of how well the brain trust responded to the evidence, with one participant calling the reaction “mixed at best,” but another saying that there was agreement that the prosecutors had credible evidence to support charges and that no one recommended against a case.The deliberations led prosecutors to simplify the charges they planned to seek to make it easier to win a conviction, and Mr. Vance was soon persuaded. Three days later, Mr. Dunne sent the team an email announcing that they would proceed. The plan, he said, was to seek charges from the panel in the spring. Most of the remaining career prosecutors were on board. But that week, a third prosecutor left the investigation into Mr. Trump.‘Time Is of the Essence’Carey Dunne, Mr. Vance’s general counsel. A leader, with Mr. Pomerantz, of the Trump inquiry, Mr. Dunne became frustrated, and he ultimately resigned, over questions about the strength of the case.Jefferson Siegel for The New York TimesWith Mr. Vance about to leave office, the investigators’ attention turned to their future boss.Born in Harlem and educated at Harvard, Mr. Bragg won a hotly contested Democratic primary last year with a campaign that balanced progressive ideals with public safety. He had served as a federal prosecutor in Manhattan and also in the state attorney general’s office, where he rose to become a top deputy managing hundreds of lawyers.Understand the New York A.G.’s Trump InquiryCard 1 of 6An empire under scrutiny. More