Senior Enforcement Counsel Kevin Wallace of the New York attorney general's office will lead the direct examination of Donald Trump when the former president takes the stand this morning.

Wallace led the depositions of Trump during the New York attorney general's investigation and also delivered the state's opening statement in the trial.

"The defendants were lying year after year," Wallace said in his opening statement.

A constant presence in court during the trial, Wallace joined the New York AG's office in 2018 after working in the private sector for 15 years.

Wallace and Trump sparred for hours during Trump's April deposition, according to a transcript of the deposition that was subsequently released by the AG's office.

"We're going to be here until midnight if your client answers every question with an eight-minute speech," Wallace remarked after one of Trump's lengthier answers.

Wallace tried to press Trump on spreadsheets that Wallace displayed during the deposition, promoting frequent objections from Trump's lawyers.

"Oh my God -- are you people capable of reading a spreadsheet?" an exasperated Wallace said after one objection from Trump's attorney Chris Kise.

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.