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.

State attorney Kevin Wallace is expected to complete his cross-examination of the defense's expert witness Robert Unell, who yesterday provided the most direct challenge to the state's analysis that found that Donald Trump's misstatements cost his lenders $168 million in lost interest.

New York Attorney General Letitia James is expected to use that lost interest analysis to justify part of the fine she wants to levy against Trump -- also known as a disgorgement -- for his allegedly ill-gotten gains.

Unell testified yesterday that he found the lost-interest analysis conducted by the state's expert Michiel McCarty was inaccurate based on real-world market conditions, including the interest rates used by commercial real estate lenders who are "living and breathing these deals daily."

"I have not seen anything to indicate that was an accurate interest rate," Unell said about the interest rates in the state's analysis.

Judge Arthur Engoron twice interjected during Unell's testimony to suggest that Trump still cost his lenders money, referring back to his partial summary judgment in which he said, "The less collateral for a loan, the riskier it is, and a first principal of loan accounting is that as risk rises, so do interest rates."