Donald Trump erupted on the witness stand during his testimony under oath in his civil fraud trial on Monday, calling the judge a "fraud" for not agreeing that Mar-a-Lago was worth more than $1 billion.

With the future of his business empire at stake in the trial, it was this weeks-old, imaginary slight — his false belief that the trial judge had "valued" his Palm Beach home and club at $18 million — that prompted Trump's loudest complaint while testifying.

What the judge had actually done — and this was five weeks ago — was mention that a decade-old tax assessment had listed Mar-a-Lago's worth at $18 million. That didn't stop Trump from crying fraud on Monday.

"The fraud is on the court when you rule that Mar-a-Lago is worth $18 million," Trump said. "I could give you a quarter of a tennis court that's worth more than that."

"He ruled against me without knowing anything about me," Trump ranted on the stand.

Trump appeared to be referring to an earlier ruling by New York Supreme Court Judge Arthur Engoron, who's presiding over the civil trial, now in its sixth week, in a downtown Manhattan courtroom.

Engoron had noted in a summary-judgment ruling that officials in Palm Beach, Florida, where Mar-a-Lago is located, appraised the property's market value at between $18 million and $27.6 million. Trump and his allies have seized on that part of the opinion, falsely claiming that Engoron had personally valued Mar-a-Lago at $18 million.

The stakes for Trump are high. The New York attorney general's office has accused Trump, his two eldest sons, and other Trump Organization executives of falsifying property valuations to receive favorable loan terms and lower tax payments. Prosecutors are looking to recoup more than $250 million from the Trump Organization and to ban Trump and his adult sons from running businesses in New York, among other penalties.

But on the witness stand on Monday, Trump was fixated on Mar-a-Lago. He insisted his social club, which is also his main residence, was worth between $1 billion and $1.5 billion.

Trump's grievance-filled speech about the market value of Mar-a-Lago was in response to a yes-or-no question about whether his statement of financial condition, a document given to banks when asking for a loan, was correct.

Kevin Wallace, the lawyer for the attorney general's office, asked again.

Trump's lawyer Alina Habba objected. "Asked and answered."

"No! It hasn't been answered!" Engoron shouted in response.

"Your honor, I'm not screaming," Habba responded.

Trump smiled at his lawyers during the exchange.

The former president and the 2024 Republican front-runner became more agitated when talking about Mar-a-Lago's value than at any other point in his testimony on Monday. He crossed and uncrossed his arms and used the topic as a springboard to attack New York Attorney General Letitia James.

In court, Trump claimed his company's financial statements were "very conservative" and that Mar-a-Lago was worth much more than what the judge and James claimed.

The statements, he said, don't include "brand value" that makes his properties worth more.

"This is the opposite of fraud. The fraud is her," Trump said, referring to James. "She said it's worth 25 million. He said it's worth 18 million. It's worth a billion dollars — or more."

On the first day of the trial, which Trump attended, Engoron had chastised Trump and members of the media who misrepresented his earlier ruling.

"I specifically said in the summary-judgment decision, I'm not valuating properties," Engoron said. "Please, press, stop saying I'm valuing it at $18 million. There was a tax assessment in that range."

On Monday, Trump said the decision was "fraudulent" and that "the fraud is on behalf of the court."

He also took the opportunity to attack President Joe Biden.

"How do you rule that I'm a fraud when, as the president of the United States, I did a great job," Trump said. "And you have to look at the current president, what he's doing."

"Done?" Wallace asked Trump.

"Done," Trump responded.

A few minutes later, Trump returned to attacking James' lawsuit. He bemoaned her allegation that he inflated the value of one of his properties, 40 Wall Street.

"She doesn't even know what 40 Wall Street is," he said.

The building is located around the corner from the New York attorney general's office.