Donald Trump was held in contempt of court Tuesday and fined $9,000 for repeatedly violating a gag order that barred him from making public statements about witnesses, jurors and some others connected to his New York hush money case. If he does it again, the judge warned, he could be jailed.

Prosecutors had alleged 10 violations, but New York Judge Juan M. Merchan found there were nine. Trump stared down at the table in front of him as the judge read the ruling, frowning slightly.

It was a stinging rebuke of the presumptive Republican presidential nominee’s insistence that he was exercising his free speech rights and a reminder that he’s a criminal defendant subject to the harsh realities of trial procedure. And the judge’s remarkable threat to jail a former president signaled that Trump’s already precarious legal standing could further spiral depending on his behavior during the remainder of the trial.

Merchan wrote that he is “keenly aware of, and protective of,” Trump’s First Amendment rights, “particularly given his candidacy for the office of President of the United States.”

“It is critically important that defendant’s legitimate free speech rights not be curtailed, that he be able to fully campaign for the office which he seeks and that he be able to respond and defend himself against political attacks,” Merchan wrote.