His composure boosted the prosecutors’ case, and his testimony was bolstered by a weak cross-examination from Mr Trump’s legal team on day one, experts said.

Mr Trump’s attorney, Todd Blanche, appeared disorganised at first, stumbling sometimes in his questioning, experts told the BBC.

But he appeared to make strides on the second day, Thursday, casting doubt on details of Cohen’s testimony, including an October 2016 phone call Cohen made to Mr Trump’s bodyguard in which he claimed to have to talked to Mr Trump about details of the hush-money payment.

It was a reminder of what experts said was one of prosecutors’ largest problems: Cohen’s credibility. The defence hammered home the point that Cohen is a convicted criminal, who spent time in prison after being convicted on several charges including lying to Congress.

Cohen was able to testify to a key part of prosecutors’ case – Mr Trump’s direct knowledge of the hush-money payment reimbursement scheme.

Cohen said former Trump Chief Financial Officer Allen Weisselberg – currently serving a perjury sentence at Rikers Island prison – decided to classify reimbursements from Mr Trump’s account as legal expenses. Cohen testified that he heard Weisselberg get the OK from Mr Trump himself.

As Cohen spoke, prosecutors also displayed the dozens of cheques, ledgers and invoices at the heart of the 34-count indictment.

But Cohen’s story may not sway all jurors.

“You are relying on a witness who in many respects … comes with a larger load of baggage than others,” Ms Rendelman said. “It makes it a bit more difficult to prove the case beyond a reasonable doubt.”