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.

Judge Engoron has denied a motion from the New York attorney general to preclude four expert witnesses from testifying for the defense when the defense presents it case starting on Monday.

The state had sought to preclude the four experts' testimony on the grounds that, following the testimony of the state's witnesses, the four defense witnesses were no longer relevant to the case.

"You've won the battle. We'll see if you win the war," Engoron told defense attorney Chris Kise -- though he warned Kise that he would cut off the witnesses if they try to debate facts already established in the case.

In making his ruling, Engoron reiterated his finding from his earlier summary judgment order that Donald Trump made at least ten internally contradictory claims in his statements of financial condition.

"You can't have a correct statement with these kinds of errors," Engoron said.

Kise told the court that Donald Trump Jr. will be the first witness to testify in the defense's case on Monday.

"Oh, I know him," Engoron deadpanned after the announcement.

It will mark Trump Jr.'s return to the witness box after the state put him on the stand last week.