US District Judge Tanya Chutkan reinstated the order on Sunday after prosecutors said Mr Trump had attempted to influence a likely witness in the case – former chief of staff Mark Meadows – in his recent posts on social media.
The gag order limits what Mr Trump can say about witnesses, prosecutors and court staff.
In the Truth Social post, Mr Trump raised questions about whether Mr Meadows would seek immunity from prosecutors in exchange for providing incriminating information against him.
“Some people would make that deal, but they are weaklings and cowards, and so bad for the future our Failing Nation. I don’t think that Mark Meadows is one of them, but who really knows?” Mr Trump wrote on October 24.
In her ruling on Sunday night, Ms Chutkan said: “This statement would almost certainly violate the order under any reasonable definition of 'targeting.'”
Mr Trump's lawyers have said the order is unconstitutional and indicated they will appeal.
The former president has also been fined $10,000 in a separate case in New York for violating his gag order in that trial a second time.