New York (AFP) - A former tabloid publisher who squashed potentially embarrassing stories about Donald Trump was back on the witness stand on Friday being grilled by lawyers of the former US president.

David Pecker, 72, has testified for four days in the trial of Trump, accused of falsifying business records to buy the silence of porn star Stormy Daniels about an alleged 2006 sexual encounter that could have derailed his 2016 White House campaign.

Pecker, the first witness in the blockbuster trial, has outlined under questioning from prosecutors a scheme known as "catch and kill," which involved purchasing and then burying salacious stories which could have been damaging to the real estate tycoon.

Trump, 77, the first former US president to face criminal charges, is accused of engaging in "election fraud" by having his then-personal lawyer Michael Cohen make a $130,000 payment to Daniels on the eve of the 2016 election against Hillary Clinton.

The high-stakes trial requires Trump to report to the drafty Manhattan courtroom multiple times a week, restricting his time on the campaign trail less than seven months before his likely election rematch with President Joe Biden.

Speaking to reporters in a hallway before entering court on Friday, Trump wished his wife, Melania, a happy birthday.

"It'd be nice to be with her but I'm at a courthouse for a rigged trial," he said.

Pecker, whose outlets included the National Enquirer tabloid, testified this week about a hush money payment to Karen McDougal, a former Playboy model who claimed to have had a year-long affair with Trump that was a precursor to the Daniels saga.

Pecker explained how transfers to the tune of $150,000 were made to "catch and kill" McDougal's story and suppress its publication, calling it a "large purchase" relative to the sums his company would normally pay for content.

He said payments to McDougal were disguised as services to American Media, the tabloid's parent company, to avoid violating campaign finance laws.

"We purchased the story so it would not be published by any other organization," Pecker told the jury. "We didn't want the story to embarrass Mr. Trump or hurt his campaign."

'I'm not a bank'

McDougal's story ultimately did come out, four days before the election in a scoop from The Wall Street Journal.

Pecker said Trump called him and was "very upset."

When it came to squashing Daniels' tale of her alleged sexual encounter with Trump, Pecker said he hesitated to pay for yet another story.

"I'm not a bank," he said.

The executive suggested to Cohen that he pay for it instead, which prosecutors say the then-Trump fixer did.

The specific charge facing Trump of falsifying business records stems from his reimbursements to Cohen for the payment to Daniels. 

During defense cross-examination which began on Thursday, Emil Bove, a Trump attorney sought to ruffle Pecker by noting timeline inconsistencies, while also casting the "catch and kill" tactics described by prosecutors as "business as usual."

Trump has appeared increasingly disgruntled, angry even, as the trial proceeds.

He complained Friday that the courtroom was "freezing" and that it was "on purpose I believe."

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.

He also faces charges in Florida of allegedly mishandling classified documents after leaving the White House.