Donald Trump's motorcade has arrived at the New York State Supreme Courthouse in lower Manhattan.

Court is scheduled to get underway at 10 a.m. ET, with Trump scheduled as the day's only witness.

Donald Trump, in New York, had a prep session with his lawyers Sunday ahead his testimony, sources tell ABC News.

Trump's mood during the session fluctuated between fits of anger regarding the case and being "in a good head space," according to sources.

The former president "can be a good witness if he stays focused," one source said.

Former President Trump is due in court to begin his testimony in his $250 million civil fraud trial at 10 a.m. ET.

Hundreds of members of the news media are huddled outside the New York State Supreme Courthouse ahead of Trump's arrival, with some having waited overnight.

After multiple in-court disputes about communications between him and his law clerk, Judge Arthur Engoron modified his limited gag order to cover attorneys in former President Donald Trump's civil fraud trial.

"Defendants may reference my staff as is appropriate to ask about scheduling issues or the management of the trial, which is an integral part of their jobs. What they may not do is to make any further statements about internal and confidential communications (be it conversations, note passing, or anything similar) between me and my staff," Engoron wrote in his supplemental limited gag order on Friday.

Engoron wrote that defense lawyers Chris Kise, Alina Habba, and Clifford Robert made "repeated, inappropriate remarks about my Principal Law Clerk, falsely accusing her of bias against them and of improperly influencing the ongoing bench trial."

The attorneys have raised multiple arguments during the trial that Engoron and his clerk passing notes between each other suggests impropriety and is distracting. Going forward, if the lawyers want to object to communications with his clerk, Engoron advised that they refer to the order as a "blanket statement."

"This gag order is as narrowly tailored as possible to accomplish its purpose, which is to protect the safety of my staff and promote the orderly progression of this trial," Engoron said.

To justify the safety threat, Engoron added that his chambers has received "hundreds of harassing and threatening phone calls, voicemails, emails, letters, and packages" since the start of the trial,

The judge threatened "serious sanctions" for violations of the extended order.

Donald Trump's accounting expert snapped at a lawyer for the New York attorney general after the lawyer suggested his opinion was bought by the defense team.

As accounting expert Eli Bartov was testifying about Trump's use of disclaimers in his financial statements, state attorney Kevin Wallace interjected, saying, "This is pure speculation from someone they hired to say whatever it is they want."

Still in the witness box, Bartov began yelling at Wallace about the comment as Trump sat watching a few feet away.

"You make up allegations that never existed," Bartov shouted. "I am here to tell the truth. You ought to be ashamed of yourself for talking like that."

Bartov, in his testimony, said that Trump's use of disclaimers functioned "just like the warning from the surgeon general on a box of cigarettes."

The accounting expert said that Trump's disclaimers clearly flagged to his lenders that they should conduct their own due diligence regarding the figures, rather than rely on them at face value. Witnesses from Deutsche Bank -- Trump's primary lender during the 2010s -- previously testified that they conducted due diligence and significantly undercut the valuations Trump provided in his financial statement when deciding to offer him loans.

"I never saw anything that is clearer than that," Bartov said about the language in Trump's disclaimer clause. "Even my nine-year-old granddaughter Emma would understand this language."

In his pretrial summary judgment ruling, Judge Engoron dismissed Trump's argument that disclaimer clauses protect him from allegations of fraud. While multiple defense witnesses have attempted to rebut Engoron's opinion about Trump's use of disclaimer clauses, the judge has signaled he stands by his opinion.

"My summary judgment is the law of the case on the legal effect of this paragraph or these sentences," Engoron said in response to Bartov's testimony, adding that the clauses "would not insulate the client."

Nevertheless, Trump attorney Chris Kise requested that Engoron reconsider his finding.

"I am fairly liberal in reconsidering my opinions," Engoron said before Bartov resumed his testimony.