As Michael D. Cohen prepared to take the stand at the civil fraud trial of Donald J. Trump this week, two women who shared an intense interest in his testimony slipped into the courtroom.
One was Susan Hoffinger, who is overseeing the Manhattan district attorney’s separate criminal case against Mr. Trump, which accuses him of concealing hush-money payments to a porn star. The other was Susan Necheles, who will help defend him against those charges.
They were there not as spectators, but as scouts: to see how Mr. Cohen — a star witness in the most important case that either lawyer has ever handled — might perform under pressure.
The result was decidedly mixed.
On his first day of testimony in the civil case, Mr. Cohen landed some blows on Mr. Trump as he calmly recounted committing crimes on the former president’s behalf. His testimony supported the central contention of the trial, which stems from a lawsuit brought by New York’s attorney general: that Mr. Trump inflated the values of his assets to boost his net worth.
Mr. Cohen’s second day was bumpier. Under questioning from one of Mr. Trump’s lawyers, Mr. Cohen appeared flustered and admitted to several past lies, including before a judge when he was sentenced to prison for federal crimes in 2018.
The two-day spectacle offered a preview of how Mr. Cohen, who once idolized Mr. Trump but now loathes him, might perform on the bigger stage of the criminal trial. It also captured the trade-offs for prosecutors of calling a witness like Mr. Cohen, a felon who can nonetheless offer an insider’s account of Mr. Trump’s conduct.
Ms. Hoffinger, Ms. Necheles and Todd Blanche, another lawyer for Mr. Trump who also attended the civil fraud trial, can use the testimony this week to inform how they navigate Mr. Cohen’s role in the criminal case brought by the Manhattan district attorney, Alvin L. Bragg. Unlike the civil fraud trial, which is being decided by a judge, the criminal case will play out before jurors who will evaluate Mr. Cohen’s credibility for themselves, magnifying the scrutiny.
One option for Ms. Hoffinger would be to extensively prepare Mr. Cohen before the trial, which is scheduled to begin in late March, though it may be pushed to a later date.
In the civil case, Mr. Cohen took the stand without preparing for the testimony with lawyers from the attorney general’s office, according to two people with knowledge of the matter. Mr. Cohen became so worried about the lack of assistance that his lawyer, E. Danya Perry, prepared him to object on his own behalf.
Ms. Hoffinger is more likely to take a hands-on approach. Her office had already interviewed Mr. Cohen more than a dozen times before Mr. Trump’s indictment, vetting his story for months, and prosecutors have gathered testimony that could corroborate much of his account.
In the civil case, Mr. Cohen was more of a peripheral witness, headline-grabbing but inessential to winning. But he is at the heart of the criminal case.
It was he, as Mr. Trump’s fixer, who paid the hush money to the porn star, Stormy Daniels. He and Mr. Trump discussed the payment to Ms. Daniels, prosecutors say, and in a separate conversation that was recorded, they spoke about another hush money deal with a former Playboy model, Karen McDougal. There are also documents and phone records that will directly match some of what Mr. Cohen is expected to say about the hush money deals.
Former prosecutors said those records could bolster Mr. Cohen’s credibility, even if jurors dislike him or have concerns about his 2018 guilty plea to numerous felonies, some connected to the deals.
“The jury might find him detestable and despicable as an individual,” said Daniel J. Horwitz, a criminal defense lawyer who spent nearly a decade as a prosecutor in the Manhattan district attorney’s office and previously represented Ms. McDougal. “But they may choose to believe him because when he says, ‘I had conversations with Donald Trump about paying hush money to Stormy Daniels,’ it’s backed up by other witnesses and other pieces of evidence.”
Cooperating witnesses are seldom choir boys. In order to have knowledge of a crime, they’re often either criminals themselves or people who were present when crimes were committed.
Prosecutors typically try to pre-empt attacks on such witnesses by asking them questions about their vulnerabilities so the jury is prepared for the worst. A witness then can discuss the facts in the best possible light.
In the civil case, a lawyer from the attorney general’s office who questioned Mr. Cohen, Colleen Faherty, used that strategy in some instances: For example, she made sure to question Mr. Cohen about the federal crimes to which he had pleaded guilty. Some, including counts related to the hush money, he still admits he committed. But he has said that he should not have been prosecuted for others related to his personal finances, despite his guilty pleas.
A lawyer for Mr. Trump, Clifford S. Robert, was able to rattle Mr. Cohen on that point, insisting that his subsequent disavowal of those crimes meant that he had lied when pleading guilty. Mr. Cohen at first said he could not remember.
“You don’t recall whether you lied at your sentencing?” Mr. Robert asked.
“I don’t recall. I have no idea what you’re talking about,” Mr. Cohen responded.
Eventually, Mr. Cohen admitted he did recall.
“Now you remember?” Mr. Robert asked.
“Yes, I do,” Mr. Cohen said.
“And you lied?”
“I did.”
When Ms. Faherty, the attorney general’s lawyer, first questioned Mr. Cohen, she did not address a key point: whether Mr. Trump had explicitly directed him to manipulate financial statements. Although Mr. Cohen has often said that Mr. Trump communicates like a “mob boss,” making his wishes known without giving explicit directions, that was not made clear in his testimony.
And when Mr. Robert asked Mr. Cohen for a yes or no answer about whether Mr. Trump had directed him to inflate the numbers, Mr. Cohen said “no.”
Mr. Trump threw up his hands as if he had won, and Mr. Robert asked that the case be dismissed immediately.
The judge, Arthur F. Engoron, denied the request.
“No way, no how this case is being dismissed,” Justice Engoron said, adding that “there is enough evidence in this case to fill this courtroom.”
Mr. Trump stormed out of the courtroom, and Ms. Faherty eventually asked Mr. Cohen to clarify the way Mr. Trump had made his wishes known.
After court had ended for the day, Attorney General Letitia James quickly played down Mr. Cohen’s importance.
“The defendants’ counsel attempted and failed to discredit our entire case,” Ms. James said in a videotaped statement. “But our case is the result of a four-year investigation that is based on hundreds of thousands of documents and many, many witnesses.”
Mr. Trump used his social media website to claim the case had been torpedoed. Privately, he mocked Mr. Cohen’s performance to advisers.
Mr. Cohen had a more positive review of his time on the stand. Summing up the experience in an interview on Thursday, he called it “pretty good for me — ultimately, really bad for him.”
