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.

Standing in the courthouse hallway where his father earlier railed against his civil trial, Eric Trump echoed his father's attacks on the New York attorney general and the case levied against his family, following the adjournment of court for the day.

"We have an unbelievable company. We have some of the best assets anywhere in the world. We've never had a default. We've never missed a payment," Eric Trump said of the Trump Organization.

Like his father, he described the case as politically motivated and decried the involvement of his family.

"They've dragged Don and I and Ivanka into it as collateral damage," he said.

Later, addressing reporters on the courthouse steps, he said that the state's efforts should be focused elsewhere.

"Let's get the murderers off the street. Let's take care of the crime. Let's rebuild our infrastructure. Everywhere you drive in New York, you hit a pothole and your car gets destroyed," he said.

Attorneys Chris Kise, Alina Habba and Clifford Robert are scheduled to deliver closing arguments for the defense -- in addition to former President Trump, should Judge Arthur Engoron reverse his decision to bar Trump from participating.

Multiple legal experts who ABC News spoke with described Trump's attempt to deliver a closing statement as unprecedented and potentially perilous for the former president.

"One of the old adages is, 'He who represents himself has a fool for a client,'" trial attorney and Dartmouth College senior lecturer Bruce Fredrickson told ABC News. "The thinking behind that is you lose the objectivity and impartiality that an advocate can provide on your own behalf."

Closing arguments generally allow both parties to summarize the evidence and testimony presented during the trial -- but because Trump is not a lawyer, he would only be able to speak for himself as a named defendant in the case, according to trial attorney and ABC News contributor Chris Timmons.

"There's been a lot of damage done, and I don't know how much he can do to repair it, but he certainly can make things worse," Timmons said.