The New York judge presiding over Donald Trump's historic criminal trial again found the former US president in contempt of a gag order on Monday and threatened to jail him for further violations.

Trump, 77, is charged with falsifying business records to reimburse his lawyer, Michael Cohen, for a $130,000 payment made to a porn star just days ahead of the 2016 election against Hillary Clinton.

Stormy Daniels, whose real name is Stephanie Clifford, was threatening at the time to go public with her story about a 2006 sexual encounter with Trump, a salacious revelation that could have been potentially damaging to his White House campaign.

Judge Juan Merchan held Trump in contempt of court and fined him $1,000 on Monday for a violation of the gag order prohibiting him from publicly attacking witnesses, jurors or court staff and their relatives.

Trump was also fined a total of $9,000 last week. But Merchan said these penalties were not serving as a "deterrent" and he would have to consider jail time for further violations.

"As much as I do not want to impose a jail sanction..., I want you to understand I will," Merchan told Trump, who sat silently at the defence table dressed in a dark blue suit and red tie.

"At the end of the day I have a job to do and part of that job is to maintain the dignity of the justice system," the judge said, calling Trump's defiance a "direct attack on the rule of law."

Merchan's ruling came at the start of the third week of testimony in the high-stakes trial of the Republican White House candidate, the first former president to face criminal charges.

The judge acknowledged that putting him behind bars for contempt would be a weighty decision and a logistical challenge.

Trump receives around-the-clock US Secret Service protection as a former president and Merchan said "the last thing I want to do is put you in jail."

"I also worry about the people who would have to execute that," he said.

 'Crisis'

Prosecutors then called their next witness, Jeffrey McConney, a Trump Organization executive who walked the jury through the reimbursements to Cohen for the hush money paid to Daniels.

Daniels, 45, and Cohen, 57, Trump's ex-lawyer who has become a vocal critic of his former boss, are both expected to testify at some point during the trial being held in a Manhattan courtroom.

Hope Hicks, a former close advisor to Trump, testified last week about the "crisis" that engulfed his 2016 presidential campaign after a tape emerged of him bragging about groping women.

Hicks said she was a "little stunned" by the now infamous Access Hollywood tape in which Trump was heard boasting about grabbing women's genitalia.

"There was consensus among us all that the tape was damaging, this was a crisis," she added.

Hicks was a key player in the final stages of Trump's successful 2016 presidential campaign when the hush money payments to Daniels were allegedly made.

According to prosecutors, panic over the tape triggered a Trump campaign effort to silence Daniels over her claim of a sexual encounter with the married Trump. Trump denies ever having sex with Daniels.

The trial has gripped the legal and political establishment as Trump seeks to re-take the White House from President Joe Biden in November's election.

In addition to the New York case, Trump has been indicted in Washington and Georgia on charges of conspiring to overturn the results of the 2020 election won by Biden.

He also faces charges of illegally storing huge quantities of top-secret documents taken from the White House after his presidency to his home in Florida.

Sign up to our free newsletters

Get the best updates straight to your inbox:
Please select at least one mailing list.

You can unsubscribe at any time by clicking the link in the footer of our emails. We use Mailchimp as our marketing platform. By subscribing, you acknowledge that your information will be transferred to Mailchimp for processing.