Former Trump adviser Hope Hicks testifies at his trial

Trump's former campaign press secretary Hope Hicks became the first former member of Donald Trump's inner circle to take the witness stand in his historic criminal trial on Friday.

"I'm really nervous," said Hicks as Trump, sitting just feet away, stared at her intently.

Hicks was intimately involved with the final stages of Trump's successful campaign for the White House when hush money payments to X-rated star Stormy Daniels were allegedly made.

Trump is charged with falsifying business records to reimburse his lawyer, Michael Cohen, for a $130,000 payment to Daniels just days ahead of the 2016 election against Hillary Clinton.

The trial, the first ever of a former US president, and its revelations have sent shockwaves through the legal and political establishment as Trump seeks to re-take the White House from President Joe Biden at November polls.

"I reported to Mr Trump" during the 2016 campaign, Hicks told the court on Friday, describing him as "very involved."

Hicks was asked about the now infamous Access Hollywood recording, released ahead of the 2016 election, of Trump boasting about how he would grab women by their genitalia.

She said Trump's response was that "it didn't sound like something he would say."

Hicks was mentioned in earlier testimony by David Pecker, the former publisher of the National Enquirer tabloid which has been key to the prosecution's case against Trump.

He said Hicks was present at a 2015 meeting at Trump Tower in New York at which he agreed to help Trump's nascent campaign for the Republican nomination the following year.

Hicks said that she did not recall the encounter.

Earlier this week, prosecutors urged Judge Juan Merchan to fine Trump for more violations of a gag order imposed to protect trial participants.

Merchan, who threatened Trump with jail time on Tuesday for further gag order violations, heard arguments from both sides and could issue a ruling Friday.

The judge started Friday's session by unusually addressing Trump directly, saying he wanted to "clear up (any) misunderstanding" on the gag order.

Merchan stressed that Trump had an "absolute right to testify" in court, and that the gag "only applies to extrajudicial statements... outside of court."

Trump, who had claimed that the gag order meant he would not be able to testify freely, responded "thank you."

Merchan has already fined Trump, who wore an electric blue tie and dark suit, $9,000 for violations of his gag order so far.

On Thursday Daniels' former attorney, Keith Davidson, was grilled by the ex-president's lawyers. Davidson also represented another woman, Karen McDougal, who claimed to have had a year-long affair with Trump.

Trump attorney Emil Bove's questioning of Davidson quickly turned heated.

"When you were negotiating on behalf of McDougal and Daniels one of your concerns was staying on the right side of the law with regard to extortion," Bove said.

"I suppose so," Davidson replied. "I did everything I could to make sure my activities were lawful."

The court also heard from a forensic expert, Douglas Daus, who examined Cohen's cell phones and retrieved what appeared to be recordings of Trump, and Cohen's phone calls.

"Merchan is doing everything in his power to make this trial as salacious as possible," Trump posted online ahead of court Friday after a series of withering posts were read into the court record on Thursday.