Jury selection is scheduled to start this week in New York City.
The president regularly demeans members of the judiciary, suggesting they should serve him, not the country.
The ruling in California comes just hours after a Trump-appointed judge in Washington, D.C., declined to block the rule.
Lori Loughlin and Anna Delvey have brought attention, once again, to the importance of style in the courtroom.
Hollywood actresses Felicity Huffman and Lori Loughlin appeared in court in Boston along with some of the other defendants.
Courts have ruled that state laws requiring truth in political advertising infringe on free speech rights.
The judge, citing a Trump post, rebuts arguments that the suit will be too much of a distraction for the president.