Testifying for a third day on Friday, Pecker, 72, agreed with a prosecutor who asked whether it would have been "National Enquirer gold" to publish the story of former Playboy model Karen McDougal's claim that she had an affair with Trump in 2006 and 2007.
But Pecker said he opted not to run the story after paying McDougal for it, because it would have hurt the Republican Trump's chances of winning the election over Democrat Hillary Clinton.
"You killed the story because it helped the candidate, Donald Trump?" prosecutor Joshua Steinglass asked him.
Pecker said yes.
Judge Juan Merchan listens as David Pecker testifies in Manhattan criminal court. (AP PHOTO)
The exchange bolstered previous testimony in which Pecker said he worked with Trump's campaign to suppress allegations of adultery at a time when the then-presidential candidate was facing multiple accusations of sexual misbehaviour.
Pecker was the first witness in the case, which accuses Trump, 77, of falsifying business records to cover up a hush money payment to porn star Stormy Daniels. Trump has pleaded not guilty.
Pecker testified his tabloid paid for the rights to two such stories he never published, a tabloid practice referred to as "catch and kill." Pecker also alerted Trump that Daniels was looking to sell her story of a sexual encounter with Trump.
The defence argues the hush money payment was made to spare Trump's family embarrassment, not to protect his presidential campaign. Trump, a businessman whose first public office was the White House, denies an encounter took place.
After Pecker's testimony, prosecutors called two more witnesses to boost their case.
Rhona Graff, who worked as Trump's business assistant from 1987 to 2021, testified she once saw Daniels at Trump Tower before he ran for president. She said she heard Trump say he was interested in casting her on The Apprentice, the reality TV show he hosted.
She said the email addresses of Daniels and McDougal were stored in the computer systems of Trump's company.
Trump shook her hand when she left the witness stand.
Banker Gary Farro testified that Trump's lawyer, Michael Cohen, set up accounts with him shortly before the election for two shell companies, including one that was used to pay Daniels.
Prosecutors say Pecker's arrangement with Trump corrupted the 2016 election. He agreed to cooperate to avoid criminal charges.
Trump is the first former president to face criminal charges. The trial, which is expected to run through May, could be the only one of his four criminal prosecutions to be completed before his November 5 election rematch with Democratic President Joe Biden.
One of those cases, which charges Trump with trying to overturn his 2020 loss to Biden, has been delayed for months by the US Supreme Court, which signalled on Thursday that it might be open to giving him some immunity from criminal charges.
Justice Juan Merchan, who is hearing the New York hush money case, has yet to rule on a request by prosecutors to punish Trump for allegedly violating a gag order that bars him from publicly criticising witnesses, some court officials and their relatives.
Merchan said he would hold a hearing next Thursday to examine what prosecutors say are further gag order violations. Trump could be fined $US1000 ($A1500) for each violation or jailed, though prosecutors say they are not seeking imprisonment at this point.
The trial is scheduled to resume on Tuesday.
