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 Jr. struggled to answer questions when pressed about why former Trump Organization CFO Allen Weisselberg departed the family's firm.

"Because some legal issues he got himself into," Trump Jr. said, declining to offer specifics about Weisselberg's guilty plea on tax evasion charges last year.

Previously giving lengthy answers to questions about his background and even smiling with the judge, Trump Jr. appeared tense on the witness stand as he answered questions about Weisselberg.

"The specific event was he was indicted," Trump Jr. said.

He added that when began working for the Trump Organization as an executive vice president in the 2010s, Weisselberg outranked him. Trump Jr. would seek Weisselberg's approval for certain business decisions such as refinancing loans.

"Who is above you in your role as an executive vice president in the Trump Organization?" state attorney Colleen Faherty asked.

"Obviously I would have reported to my father in that period of time … people like Allen Weisselberg would have still been senior to me," Trump Jr. said of that time period.

Trump Jr. said he gained more responsibility in 2016 when his father became president and he was named a trustee of his father's revocable trust. He said that he, Weisselberg and his brother Eric Trump became a kind of triumvirate running the Trump Organization.

"We stopped reporting to my father on decisions involving the business," Trump Jr. said.

That relationship broke down once Weisselberg got himself into "legal issues," Trump Jr. said. He testified that he could not recall the circumstances of Weisselberg's exit, including the multimillion-dollar severance deal that Weisselberg received, which Weisselberg faced questions about during his own testimony earlier this month.

"I have no knowledge of the specifics of how it happened. He is no longer working at the Trump Organization," Trump Jr. said of the former CFO.