For five years, Michael D. Cohen has waged battle with Donald J. Trump from afar: on social media, on cable television and in the pages of his books.
But on Tuesday, Mr. Cohen confronted his onetime boss from the witness stand in a Manhattan courtroom, attacking the former president as a criminal and a cheat and defending his own credibility under a barrage of questions.
Mr. Cohen, once Mr. Trump’s loyal fixer and now his antagonist, was testifying in a civil fraud case that threatens to upend the former president’s family business and undermine his public image as a businessman. It was the first time the men had come face to face since 2018, and the reunion was tense. Mr. Trump, seated feet away at the defense table, scoffed and shook his head in apparent frustration.
Mr. Cohen had been called to testify about Mr. Trump’s annual financial statements, which are at the heart of the civil case that the New York attorney general, Letitia James, brought against Mr. Trump. Mr. Trump, Mr. Cohen testified, directed him to “reverse engineer” the statements to reach the former president’s desired net worth.
Although Mr. Cohen had leveled similar accusations before, he had not, until now, made them in the presence of the former president, a man he once idolized. Mr. Cohen nonetheless began calmly and in a clear voice, his New York accent emphasizing his statements about his role at the Trump Organization, where he reported directly to Mr. Trump.
“I was tasked by Mr. Trump to increase the total assets based upon a number that he arbitrarily elected,” Mr. Cohen testified, saying that it was his responsibility to “increase those assets in order to achieve the number.”
Later in the day, the temperature rose when Mr. Cohen was cross-examined by one of Mr. Trump’s lawyers, Alina Habba. She called Mr. Cohen’s credibility into question, noting that he had admitted to lying under oath when he pleaded guilty to federal crimes in 2018, wrongs that he had said he committed on Mr. Trump’s behalf.
“You have lied under oath numerous times, Mr. Cohen — isn’t that correct?” Ms. Habba asked, referring to his previous guilty pleas.
“That’s correct,” Mr. Cohen said.
Their exchange devolved. Several times, Mr. Cohen made legal objections from the witness stand; in a trial, only lawyers trying the case can make objections. At other times, he refused to respond to questions, saying instead, “Asked and answered.” Mr. Cohen, who has lost his law license, even cited court cases in his defense.
The cross-examination is expected to continue Wednesday.
The reunion of Mr. Trump and Mr. Cohen took place on a stage that has become familiar to them both: a courtroom. In the years since their last encounter, Mr. Cohen has gone to prison and testified against Mr. Trump before Congress and a grand jury. For his part, Mr. Trump, who has called Mr. Cohen a “rat” and a liar, has been impeached twice, voted out of office and indicted four times.
The buildup to the testimony had the hype of a heavyweight fight. When Mr. Cohen delayed, citing a health problem, Mr. Trump claimed that Mr. Cohen “didn’t have the guts.” Mr. Cohen fired back, posting a mocked-up image of himself and the former president captioned “Let’s get you back to your cell.”
During a midday break Tuesday, Mr. Cohen acknowledged the tension. “Heck of a reunion,” he said.
And after court ended, Mr. Trump gave his own review of the testimony, declaring that Mr. Cohen had been “totally discredited” and was a “disgraced felon.”
Mr. Cohen’s appearance is expected to kick off a more explosive phase of the trial, which began three weeks ago. Ms. James has accused Mr. Trump of inflating the value of his assets by billions of dollars to obtain favorable treatment from banks and insurance companies.
The judge, Arthur F. Engoron, has already ruled that Mr. Trump fraudulently misvalued his properties. The trial will determine whether he has to pay a hefty penalty and whether his conduct violated other laws.
With the central claim resolved, the trial had been a tedious proceeding, punctuated by Mr. Trump’s occasional visits, during which he used the camera-lined courthouse hallway as a campaign stop in his run for another term in the White House.
His lawyers have made it clear that they will appeal key rulings by Justice Engoron, who will decide the case. There is no jury. The lawyers have argued that valuations are subjective and that others were to blame.
Mr. Cohen’s testimony before Congress in 2019 that the former president’s company had manipulated financial statements was the impetus for Ms. James’s investigation. He said Trump Organization employees would start with Mr. Trump’s desired net worth and then compute the value of the assets to match it.
He reprised some of those comments on Tuesday. But the substance of his testimony paled in comparison to the drama of the face-off. Mr. Cohen’s future appearances may test Mr. Trump’s courtroom decorum; Justice Engoron has already imposed a $5,000 fine on him for violating a gag order.
The judge acted after Mr. Trump posted a picture on social media of Justice Engoron’s law clerk, Allison Greenfield, with Senator Chuck Schumer, falsely labeling her “Schumer’s girlfriend.” When the Trump campaign failed to remove the post from its website, Justice Engoron levied the fine and threatened to hold Mr. Trump in contempt and even jail him for future violations.
The order applies only to comments about the judge’s staff, but Justice Engoron may also object to threats to Mr. Cohen or other witnesses. Yet threats are the defining feature of Mr. Trump and Mr. Cohen’s relationship.
Mr. Cohen went to work for Mr. Trump in 2007 and embraced the role of attack dog. He once vowed to take a bullet for the man he referred to as “Mr. Trump.”
That all changed in 2018, when Mr. Cohen became the target of a federal investigation into his role in a hush-money payment to a porn star, Stormy Daniels. The payment, which Mr. Cohen made during the 2016 campaign, blocked Ms. Daniels from telling her story of an affair with Mr. Trump years earlier — an affair that Mr. Trump denied had ever taken place.
In one of their final encounters, Mr. Cohen visited Mr. Trump’s Mar-a-Lago estate in Florida in March 2018. The F.B.I. searched Mr. Cohen’s home and office soon after.
With Mr. Cohen facing legal bills and prison, Mr. Trump began to distance himself from his fixer, who soon lashed out and began to speak with prosecutors.
When Mr. Cohen pleaded guilty to campaign finance violations in 2018, he said in court that he had paid Ms. Daniels at Mr. Trump’s direction.
Federal prosecutors declined to indict the former president. But Mr. Cohen, who served a little more than a year in prison, repeated his accusations to their state counterparts at the Manhattan district attorney’s office. In April, the Manhattan prosecutors announced charges against Mr. Trump related to the deal.
Mr. Cohen is expected to be a star witness in that criminal trial, which could start in the spring. On Tuesday, Susan Hoffinger, the head of investigations for the office, sat in the back of the courtroom to see Mr. Cohen’s testimony firsthand. Todd Blanche, who is representing Mr. Trump in that case, was also present.
In Tuesday’s testimony, Mr. Cohen said that he had provided valuations for at least six of Mr. Trump’s assets, including a residential tower known as Trump Park Avenue, and the Miss Universe pageant. Throughout the day, Mr. Cohen was questioned by Colleen Faherty, a lawyer from the attorney general’s office, who steered him through his years of financial statements.
He spoke of other members of the Trump Organization, and specific transactions in which he had been involved. Always, he returned to his old boss. He made sure the courtroom knew that, as he put it at one point, “all final decisions were done by Mr. Trump.”
He had less of an opportunity to vent about the former president when questioned by Ms. Habba. At one point, when Mr. Cohen attempted to provide a lengthy answer to a straightforward question, Ms. Habba asked him to stop.
“You’re not in your podcast, and you’re not on CNN,” she said. “You’re here with me.”