The two have crossed paths before, legally speaking.
Justice Juan Manuel Merchan presided over the 2022 tax-fraud trial that led to the conviction of the Trump Organization’s chief financial officer, Allen Weisselberg.
He is also the judge for the fraud and money-laundering case against Steve Bannon, a staunch Trump ally.
The New York County Supreme Court judge has served 17 years on the bench, but this is by far the most high-profile case to cross his courtroom.
Mr Trump has slammed him on social media, repeatedly accusing Justice Merchan of corruption and harbouring hate against the former president. Mr Trump has made similar accusations against various judges and prosecutors across his civil and criminal trials.
Mr Trump will soon hear the verdict in his hush-money trial, where he faces 34 felony charges for allegedly falsifying business records.
He denies all wrongdoing, and he says he never had sex with adult-film star Stormy Daniels – who allegedly received the $130,000 payoff.
A soft-spoken but stern jurist
Justice Merchan is known for his reserved nature. He is not a loud man, which can make it a bit difficult to hear him when he makes an important decision in court, but he is no pushover, either.
Throughout the trial, he has pushed back against Mr Trump and his legal defence team when they have tried to challenge the former president’s gag order or attempted to expand the parameters of his direction and instructions.
The judge fined Mr Trump $1,000 for the 10 times he was found to have violated the order – a motion that prohibited the former president from speaking about the witnesses, jurors and others involved in the case.
He also warned that, as “a last resort, he would consider jailing the defendant for further infractions. Justice Merchan said he knew the fines had a limited effect because of Mr Trump’s wealth.
“Mr Trump, it’s important to understand that the last thing I want to do is to put you in jail,” Merchan said in court. “You are the former president of the United States and possibly the next president, as well.”
That threat appears to have mollified Mr Trump in the interim, but it was not the only time the judge would address bad behaviour in his courtroom.
Justice Merchan cleared the courtroom and scolded the case’s final witness – Robert Costello – who the defence had called to rebut claims made by Michael Cohen, Mr Trump’s former lawyer.
Mr Costello is an outspoken critic of the case, and while on the stand, he audibly said “jeez” in response to the judge sustaining multiple objections from prosecutors, which cut off his responses.
After sending out those seated in the benches, he chastised the former federal prosecutor about “proper decorum in my courtroom”.
“You don’t say ‘jeez’. And then if you don’t like my ruling, you don’t give me side eye, and you don’t roll your eyes,” he told the witness.
The $15 Joe Biden donation
Soon after Mr Trump was arraigned, records emerged showing Justice Merchan had donated a total of $35 to Democrats during the 2020 election.
That included a $15 donation to Joe Biden’s campaign, NBC News reported, as well as $10 donations to groups called the “Progressive Turnout Project” and “Stop Republicans”.
New York state, following the American Bar Association’s guidance, prohibits judges from making contributions to political organisations or candidates.
Even though the donation to Mr Biden and, possibly, the one to Stop Republicans, would be forbidden, they would be “viewed as trivial, especially given the small sums”, Stephen Gillers, an expert on legal ethics at New York University, told BBC News.
Justice Merchan did not recuse himself over the donations and the issue has since died down.
Daughter has worked for Democrats
The judge’s daughter, Loren Merchan, has been at the centre of a bigger conflict-of-interest storm.
Ms Merchan is president of Authentic Campaigns, a firm that has worked on digital fundraising and advertising for Democratic clients, including Mr Biden and Representative Adam Schiff, who led impeachment efforts against Mr Trump.
Mr Trump has pushed to have the judge removed from the case, citing Ms Merchan’s work, but those attempts have failed.
Justice Merchan consulted with the New York State Advisory Committee on Judicial Ethics, which determined “the matter currently before the judge does not involve either the judge’s relative or the relative’s business, whether directly or indirectly”.
With that established, the judge has declined to recuse himself from the case.
Mr Trump also blasted Ms Merchan on social media, which caused Manhattan District Attorney Alvin Bragg to request an expansion of the former president’s gag order to include the judge’s family.
Justice Merchan approved the request. The order already banned comments about witnesses, jurors, court staff, lawyers for the prosecution, and their families. It does not bar Mr Trump from speaking about the judge or Mr Bragg, who is leading the prosecution of the case.
Comments about Ms Merchan could cause the judge to worry about the safety of his “loved ones”, he wrote, which would “undoubtedly interfere with the fair administration of justice”.
Mr Trump has decried the gag order as violating his constitutional right to free speech.
Who appointed Judge Juan Merchan?
Justice Merchan began his legal career in 1994, when he graduated from Hofstra University School of Law.
He worked as a prosecutor, serving in the New York County District Attorney’s Office and as an assistant attorney general in both Nassau and Suffolk counties, before being appointed a family court judge 2006.
Justice Merchan has served at the New York County Supreme Court, presiding over criminal matters, since 2009.
“He’s a serious jurist, smart and even-tempered,” Manhattan defence attorney Ron Kuby told NBC News. “He’s not one of those judges who yells at lawyers, and is characterised as a no-nonsense judge. But he’s always in control of the courtroom.”
In the case against the Trump Organization, Justice Merchan was adamant that the charges were absolutely not politically motivated.
The organization’s lawyer argued Mr Weisselberg was being targeted because of his association with the former president.
