Former US President Donald Trump has been held in contempt of court for violating a gag order for the 10th time in his hush-money trial in New York.
Justice Juan Merchan issued his most serious warning yet to Mr Trump, saying further violations could mean jail.
"At the end of the day, I have a job to do and that job is to protect the dignity of the judicial system," the judge said.
This is the second gag order ruling of the trial.
Earlier in the hush-money proceedings, Judge Merchan sided with the prosecution and fined Mr Trump $1,000 each for nine violations.
Mr Trump has pleaded not guilty to 34 counts of falsifying business records to conceal a payment to a porn actress to hide an alleged sexual encounter. He has denied all wrongdoing.
On Monday, the third week of testimony in the first-ever criminal trial of a former president, Justice Merchan said it appeared the $9.000 gag-order fine from the previous infractions was not serving as a deterrent.
"Therefore going forward this court will have to consider a jail sanction," he said. "It is important that you understand that the last thing I want to do is put you in jail."
Prosecutors said last week they were "not yet seeking jail" for Mr Trump's alleged gag order violations.
Justice Merchan acknowledged that incarcerating Mr Trump would be very disruptive to the proceedings. But he called the gag order violations "a direct attack on the rule of law" that he cannot abide.
Sitting with a stern expression at the defence table, Mr Trump showed little reaction to the threat of jail.
After court adjourned for the day, Mr. Trump called the gag order "disgraceful" and seemed defiant in the face of the warning. "Our Constitution is much more important than jail. It's not even close. I'll do that sacrifice any day,'' he said later outside the courtroom.
Prosecutors argued last week that Mr Trump's social media posts, where he suggested the jury is unfair because the area is "95% Democrat", violated the order.
The former president, a Republican, has repeatedly argued he cannot get a fair trial in overwhelmingly Democratic Manhattan.
In Justice Merchan's written ruling, he said Mr Trump was held in contempt because he made public statements about the jury and how it was selected.
He wrote: "In doing so, the defendant not only called into question the integrity, and therefore the legitimacy of these proceedings, but again raised the specter of fear for the safety of the jurors and of their loved ones."
Justice Merchan added: "Defendant is hereby put on notice that if appropriate and warranted, future violations of its lawful orders will be punishable by incarceration."
In addition to the threat of jail time, Mr Trump was ordered to pay a $1,000 fine by the end of the day on Friday. He also has to take down the offending social media post by 14:15 ET (18:15 GMT) on Monday.
Defence lawyer Todd Blanche had defended Mr Trump, arguing last Thursday that the gag order was unfair.
"Everybody can say whatever they want" about the trial, except for his client, Mr Blanche said.
"They're not defendants in this case," Justice Merchan responded. "They're not subjected to the gag order."
He pointed out that Mr Trump is allowed to speak. However, as a defendant "there are some things you can't talk about", added the judge.
Mr Blanche said Mr Trump should be able to respond to digs about the trial from President Joe Biden, his Democratic opponent in November's White House election.
The judge countered that there was nothing in the gag order that would prevent Mr Trump from doing so.
The rest of the day in court - while lacking bombshell many moments on the stand - took jurors through several documents that prosecutors consider crucial.
Each of the 34 felony charges against Trump corresponds to an invoice, ledger entry, or cheque tied to reimbursing Mr. Trump's former attorney Michael Cohen for a hush money payment Cohen made to the porn actress, Stormy Daniels. The recordings of the reimbursement is the criminal basis for the prosecution's case.
Prosecutors charge Trump broke the law by falsely recording the reimbursements to Cohen as legal expenses, and that he did so to cover up or commit a second crime.
On Monday, jurors were able to see the physical documents connected to the payments.
Witnesses explained that once Cohen's repayments started coming from Mr Trump's personal account in spring 2017, the cheques would be sent to Washington, DC for him to personally sign.
The defence, meanwhile, worked to distance Trump from the payments and undercut witness' testimony.
One witness said Trump never directly asked him to oversee the reimbursements to Cohen and another said while she knew cheques were sent to Trump to sign, she didn't know what he did with them.
Orders had not come directly from Trump, but from those who worked for him, she said.
