Donald Trump’s former fixer Michael Cohen has told jurors about an Oval Office meeting in which the then-US president confirmed a plan to reimburse Cohen secretly for a hush money payment to a porn star.

Cohen, the prosecution’s star witness at Trump’s criminal trial in New York, also acknowledged lying on multiple occasions — including under oath — but emphasised that he did so out of loyalty to Trump, as prosecutors sought to pre-empt an expected defence attack on Cohen’s credibility.

In his first day as a witness on Monday (NY time), Cohen laid out in painstaking detail how Trump ordered him to pay the adult film actress Stormy Daniels — “Just do it,” Cohen remembered Trump saying — to keep her story about an alleged 2006 sexual encounter under wraps.

Cohen’s $US130,000 ($196,350) payment in October 2016 is at the heart of Trump’s trial, the first for a former US president, now in its fifth week.

Trump, 77, the 2024 Republican presidential candidate, has pleaded not guilty and denies any sexual encounter with Daniels.

He has characterised the case as a partisan attempt to interfere with his campaign to take back the White House from Democratic President Joe Biden.

Prosecutors say Trump paid Cohen back after the election by creating false records indicating they were for legal fees.

Those disguised reimbursements provide the basis for the 34 counts of falsifying business records that Trump faces.

In testimony on Tuesday, Cohen recounted an Oval Office meeting with Trump in February 2017 when the newly inaugurated president told him he would soon be receiving the first two instalments of a bonus package.

That package, Cohen said, included reimbursements for the Daniels payment.

Trump spoke at times with his lawyer Emil Bove, seated to his left, as prosecutor Susan Hoffinger walked Cohen through a series of invoices and cheques – some signed by Trump himself – that Cohen said were falsely marked as paying to retain him for legal services.

“There was no retainer agreement, was there?” Hoffinger asked.

“No, ma’am,” Cohen replied.

Cohen, 57, said he lied multiple times to Congress during an investigation into Trump’s Russia ties, eventually pleading guilty to perjury.

He also told jurors he lied repeatedly about the payments to Daniels and another woman, telling journalists that Trump had no involvement and pressing Daniels to issue a statement denying their encounter.

Asked how he knew Daniels’ statement was false, Cohen replied, “Because I helped him craft it,” referring to Daniels’ lawyer.

In 2018, during a federal investigation into the Daniels matter, FBI agents raided Cohen’s home.

He said he called Trump in a panic.

“He said to me, ‘Don’t worry, I’m the president of the United States, there’s nothing here, everything is going to be OK, stay tough, you’re going to be OK,'” Cohen said.

That was the last time they spoke directly, Cohen added.

Cohen pleaded guilty to federal crimes in 2018, including offences related to the Daniels payment, and his chequered history is sure to draw a bruising cross-examination from Trump’s lawyers, who have already cast him as a liar.

A day after several Republican lawmakers attended the trial in support of Trump, US House Speaker Mike Johnson joined him before Tuesday’s session and later criticised the case outside the courthouse, calling it politically motivated.

While Cohen testified on Tuesday, a mid-level appeals court denied Trump’s latest effort to throw out a gag order that Trump asserted violated his right to free speech and left him unable to respond to criticisms from people like Cohen.

The order, imposed by Justice Juan Merchan, who is overseeing the trial, prohibits Trump from making public comments about jurors, witnesses and families of the judge and prosecutors if meant to interfere with the case.

On Monday, Cohen described multiple episodes in which he said Trump approved payments to keep damaging sex-scandal stories out of the public eye, lest they torpedo his presidential campaign.

“Everything required Mr Trump’s sign-off,” Cohen said.

Cohen testified that Trump was solely concerned about the impact Daniels’ story could have on his White House bid – and not, as Trump’s defence lawyers have suggested, about the effect on his wife and family.

That distinction is crucial to the prosecution’s case.