Trump’s Trial Starts Monday. It Will Spotlight What He’s Really Worth.

From his earliest days as a real estate developer to his renegade run for the White House, Donald J. Trump honed a very particular skill: the art of the boast.

“I look better if I’m worth $10 billion than if I’m worth $4 billion,” he once said, disputing his ranking on the Forbes billionaires list.

After decades of exaggerating with impunity, Mr. Trump will go on trial Monday, facing a lawsuit brought by New York’s attorney general, Letitia James, that accuses him of inflating his riches by billions of dollars and crossing the line into fraud. It will be the first of several government trials he will face in the coming year, a procession of high-stakes courtroom battles that coincide with his third White House run.

And it will be an avidly scrutinized spectacle that will lift the curtain on Mr. Trump’s reputation as a businessman, a core piece of his identity.

Ms. James’s civil case, separate from Mr. Trump’s four criminal indictments,accuses the former president, his adult sons and their family business of inflating the value of Mr. Trump’s assets to secure favorable loan terms from banks. Mr. Trump, who has denied wrongdoing, is expected to attend the opening day of the trial and eventually will be called to testify.

Before the trial even begins, Mr. Trump is losing. The New York State Supreme Court judge overseeing the case ruled last week that Mr. Trump had persistently committed fraud, deciding that no trial was needed to determine the veracity of the claims at the core of Ms. James’s lawsuit. The judge, Arthur F. Engoron, also imposed a heavy punishment, stripping the Trumps of control over their signature New York properties — a move that could crush much of the business known as the Trump Organization.

Ms. James is now asking for more from Justice Engoron, who will determine the outcome of the trial himself; there will be no jury. She wants Mr. Trump to be fined as much as $250 million and to be permanently barred from running a business in New York. If she succeeds, the former president would be unceremoniously evicted from the world of New York real estate that made him famous.

While there is no doubt that the former president is worth a lot of money, the trial will determine how much he and his adult sons exaggerated that wealth and what the ultimate consequences will be.

Howard M. Erichson​, a professor at Fordham Law School who specializes in civil procedure, emphasized that Justice Engoron’s earlier decision had already resolved the question of fraud at the heart of the case. What remained were details, he said.

“But those details are important,” he said, “Because those details determine what Donald J. Trump and the Trump Organization will be prohibited from doing, as well as the size of any civil penalty.”

Until last week, it appeared as if the trial might not start on time, or have much impact on the former president. Mr. Trump had sued Justice Engoron and Ms. James, claiming that they had ignored an appeals court decision in June that raised the prospect that some of the accusations were too old to proceed to trial. The appeals court granted a brief pause while it considered his case.

On Thursday, the appeals court rejected that last-ditch effort, clearing the way for the trial to begin.

Mr. Trump has accused Ms. James and Justice Engoron, who are both Democrats, of carrying out a political crusade against him. He has called the judge “deranged” and Ms. James, who is Black, a racist.

The former president and his sons, Donald Trump Jr. and Eric Trump, who took the reins of the family business when their father ascended to the White House, are all expected to be called to the witness stand. Ms. James has already questioned Mr. Trump twice under oath, though at one session he invoked his Fifth Amendment right against self-incrimination. A lawyer for Ms. James indicated last week that Mr. Trump will be one of the last witnesses called.

Harlan Levy, who served as chief deputy New York state attorney general under one of Ms. James’s predecessors and is now a partner at Foley Hoag, called the former president’s testimony “a wild card.”

Whether or not Mr. Trump ultimately takes the stand, Ms. James’s trial kicks off what is shaping up to be one of the most painful periods in his long public life.

In March, he will stand trial on federal criminal charges for his effort to overturn the results of the 2020 election. In May, the federal case accusing him of mishandling classified documents and obstructing the government’s efforts to wrest them back is scheduled to go to trial. And after that, he will face two criminal trials from local prosecutors: one in Manhattan, where he was charged related to hush-money payments to a porn star, and the other in Georgia, where he is accused of racketeering for trying to alter the outcome of the state’s vote in the election.

The criminal consequences in those cases are starker than the punishments Ms. James is seeking in her civil proceeding; in some of the proceedings, Mr. Trump could face years behind bars.

All the legal peril, however, has only helped him politically. Mr. Trump is running far ahead of the rest of the Republican field — his polling went up after he was first indicted this spring — and is a heavy favorite for the 2024 nomination.

Yet even as he thrives in the race, Mr. Trump faces a threat to the heart of his identity: Ms. James’s case rips away the facade of unlimited wealth that he is most proud of and that provided the platform for his political rise.

The trial will begin at 10 a.m. at the New York State Supreme Court Building on Foley Square in Lower Manhattan, which is emblazoned with the slogan “the true administration of justice is the firmest pillar of good government.”

The witness lists suggest that the trial could last months — and will involve a who’s who of Mr. Trump’s universe. More than 50 people are on Ms. James’s list — including Allen H. Weisselberg, the Trump Organization’s former financial gatekeeper who testified in the company’s criminal tax fraud trial last year and who is also a defendant in this case. The list may shrink, and although the trial was scheduled to last nearly until Christmas, it is likely to be shorter.

Presiding over it all will be Justice Engoron, a charismatic and eccentric judge who has been a thorn in the side of Mr. Trump and his lawyers for more than a year.

Justice Engoron maintains a light atmosphere in the courtroom, often ribbing the lawyers, particularly Christopher M. Kise, who represents Mr. Trump. But he has been harsh at times: Even before he removed Mr. Trump’s control of his New York companies last week, he fined the former president $110,000 for failing to comply with a subpoena. And he fined Mr. Trump’s lawyers $7,500 each for repeating arguments that he had previously rejected.

Those defense arguments essentially amounted to no harm, no foul. Mr. Trump, his lawyers argued, is accused of misleading banks that actually made money from their dealings with him. He never missed a loan payment, and the banks did not rely on the financial statements that Ms. James believes are a work of fiction.

But Justice Engoron noted in his ruling last week that a powerful state law allows Ms. James to pursue “persistent fraud” without having to show that a defendant actually intended to defraud anyone, or that their actions resulted in financial loss — a lower bar than most fraud cases. It also affords drastic remedies, empowering her to seek steep financial punishments and the cancellation of Mr. Trump’s certificates to operate a business in New York.

Justice Engoron’s decision last week went property by property — from Trump Tower on Fifth Ave to his Mar-a-Lago estate in Florida and a golf course in Scotland — concluding that Mr. Trump had in fact engaged in fraud as Ms. James said. (The accusations concern some of Mr. Trump’s properties outside New York, but any consequences would apply to his assets within the state.)

Take, for example, Mr. Trump’s triplex apartment in Trump Tower. Ms. James accused Mr. Trump of overestimating its size, saying it was 30,000 square feet, when it was actually about 11,000. Justice Engoron noted that Mr. Trump’s lawyers had “absurdly” suggested that the calculation of square footage was subjective.

“A discrepancy of this order of magnitude, by a real estate developer sizing up his own living space of decades, can only be considered fraud,” he wrote.

The matters still to be hashed out at trial will require Ms. James to show that Mr. Trump intended to commit fraud and may require her to convince Justice Engoron that the inflated financial statements were taken seriously by the banks and insurance companies that received them.

If Mr. Trump testifies, he will have to do a better job of defending himself than he did in his sworn deposition earlier this year. Justice Engoron was not impressed, as he made clear in his order last week.

“The defenses Donald Trump attempts to articulate in his sworn deposition are wholly without basis in law or fact,” the judge wrote.