Donald Trump’s former lawyer and fixer Michael Cohen took the witness stand on Tuesday to testify against the former president in a civil fraud case in New York City that threatens to break up Trump’s business empire.

Cohen has become one of Trump’s fiercest critics since cutting ties with him five years ago. He is now a key witness in a lawsuit brought by Democratic New York Attorney General Letitia James alleging Trump inflated the value of his properties by billions of dollars in statements to banks to secure better loan terms.

Colleen Faherty, a lawyer for the attorney general’s office, began her questioning by reviewing Cohen’s criminal history. Cohen in 2018 pleaded guilty to a campaign finance violation and lying to Congress. Cohen has said he committed those crimes on Trump’s behalf.

Earlier on Tuesday, Trump and Cohen traded barbs in comments to reporters upon arriving at the New York State Supreme Courthouse.

“This is not about Donald Trump vs. Michael Cohen or Michael Cohen vs. Donald Trump,” Cohen said as he arrived at the courthouse in Manhattan. “This is about accountability, plain and simple.”

Trump, the frontrunner for the 2024 Republican presidential nomination, called Cohen a “liar” minutes later.

“He’s a proven liar, as you know, a felon,” Trump told reporters before entering the courtroom, referring to Cohen. “We did nothing wrong and that’s the truth.”

Congressional testimony a catalyst

Cohen began a three-year prison sentence in 2019 but was released to home confinement the following year. He told Reuters on Monday that Trump calling him a liar amounted to “the pot calling the kettle black.”

Cohen’s testimony during a 2019 congressional probe of Trump’s finances was the impetus for James’s lawsuit.

Trump has denied wrongdoing and defended the valuations of his properties, saying the case is a “fraud” and a political witch hunt.

He has occasionally appeared in court over the past month, complaining in inflammatory remarks to reporters that it is a distraction from his campaign. He returned Tuesday after campaigning in New Hampshire.

WATCH l Highlights from Cohen’s 2019 testimony on Capitol Hill:

Featured VideoIn testimony over the course of seven hours, Michael Cohen, Trump’s former personal lawyer, characterized his former boss as a “racist,” a “con man” and a “cheat.” But he also said he had no “direct evidence” that Trump or his aides colluded with Russia to get him elected, the primary question of special counsel Robert Mueller’s investigation.

In September before the trial began, Judge Arthur Engoron found that Trump fraudulently inflated his net worth and ordered the dissolution of companies that control crown jewels of his real estate portfolio, including Trump Tower in Manhattan. That ruling is on hold while Trump appeals.

The trial concerns six other charges the organization faces. James is seeking at least $250 million US in fines, a permanent ban against Trump and his sons Donald Jr. and Eric from running businesses in New York and a five-year commercial real estate ban against Trump and the Trump Organization.

Early in the trial, Engoron barred the parties from speaking publicly about court staff after Trump shared a social media post attacking Engoron’s clerk and identifying her by name.

Trump deleted the post, but last week Engoron revealed that a screenshot had remained live on his campaign site for weeks. Engoron fined Trump $5,000 and warned that future violations would bring “far more severe” sanctions.

Cohen has also spoken about arranging hush money payments on Trump’s behalf to keep unflattering stories out of the press during the 2016 presidential election. Two of the payments went to adult film performer Stormy Daniels and former Playboy Playmate of the Year Karen McDougal, each who alleged extramarital affairs with the married Trump.

A separate, criminal case that deals, in part, with allegations that Trump falsified business records in order to conceal those payments, is set to go to trial in 2024.