Donald Trump Jr, the former president's eldest son, took the witness stand in the civil fraud trial that could cripple the family real estate business in New York state.
Mr Trump, 45, is the first member of the Trump family to testify in the case in which the Trump Organisation is accused of inflating the value of its assets by billions of dollars to obtain more favorable bank loans and insurance terms.
His younger brother, Eric Trump, 39, is also expected to testify this week and the former president himself may be questioned on Monday, a day shy of one year before the 5 November 2024 presidential election that he hopes will sweep him back into the White House.
If the 77-year-old Trump takes the stand in the Manhattan courtroom where the trial is taking place it will be the first time he testifies publicly in any of the various civil and criminal cases facing him.
Donald Jr and Eric Trump are executive vice presidents of the Trump Organisation, a sprawling network of companies managing residential buildings, office skyscrapers, luxury hotels and golf courses around the world.
The former president's daughter, Ivanka Trump, who left the Trump Organisation in 2017 to become a White House advisor to her father, is not a co-defendant in the case but has also been ordered to testify. She has appealed the subpoena.
Donald Jr, wearing a dark blue suit and pink tie and appearing relaxed, was asked by Colleen Faherty, a lawyer for the New York attorney general's office, who took the reins of the Trump Organization after his father became president in January 2017.
"A combination of myself, my brother (Eric) and Allen Weisselberg," he said in a reference to the former chief financial officer, who pleaded guilty last year to tax evasion.
Donald Jr was also asked a series of questions about accounting principles but said he did not have detailed knowledge of the subject.
"I leave it to my CPAs," he said in a reference to certified public accountants.
The court then adjourned for the day. Donald Jr is to return to the stand.
The former president and his sons do not risk going to jail in the fraud case brought by New York state attorney general Letitia James, but face up to $250 million in penalties and potential removal from management of the family company.
Prior to his son's testimony, Donald Trump lashed out at Judge Arthur Engoron, who is presiding over the case, and told him to "leave my children alone."
In a series of posts on his Truth Social platform, Mr Trump called the judge a "political hack" who is "doing the dirty work for the Democrat Party."
"Engoron is crazy, totally unhinged, and dangerous," the former president said of the judge, who has already ruled that Trump, his sons and other senior executives of the Trump Organization committed fraud.
"Leave my children alone, Engoron," Mr Trump said. "You are a disgrace to the legal profession!"
He also denied the corporate fraud charges and called the case a "witch hunt."
"The Banks and Insurance Companies were paid in full, no defaults, they all made money, and there is no Victim (except me!)" Trump said on Truth Social. "My Financial Statements are GREAT! There was no fraud."
Donald Trump also said he would appeal a partial gag order imposed by Engoron on 3 October that bars him from attacking court staff, though not the judge himself.
Engoron has fined the former president twice already, $5,000 and $10,000, for violating the order by attacking his law clerk.
Mr Trump is not required to attend the trial, but he has shown up sporadically, using his appearances to portray himself as the victim of what he claims is a Democratic plot to derail his White House campaign.
The civil fraud trial is one of several legal battles facing Mr Trump as he seeks to recapture the presidency.
He is to go on trial in Washington in March for conspiring to overturn the results of the 2020 election, and in Florida in May on charges of mishandling top secret government documents.
The twice-impeached former president also faces racketeering charges in Georgia for allegedly conspiring to upend the election results in the southern state after his 2020 defeat by Democrat Joe Biden.
