When the federal indictment against Letitia James, New York’s attorney general, became public on Thursday, her fellow New York City Democrats rushed to envelop her with support. Few matched the zeal of Zohran Mamdani.

Mr. Mamdani, the Democratic nominee in this year’s mayor’s race, accused President Trump of using “fascist tactics” to attack the “fabric of our democracy.” He stood shoulder to shoulder with other leading Democrats near Foley Square in Manhattan to defend Ms. James while criticizing the president.

Amid the outpouring of Democratic support, Mr. Mamdani made sure to point out one voice that was conspicuously muted: former Gov. Andrew M. Cuomo’s.

Mr. Cuomo on Thursday condemned Mr. Trump’s tactics without mentioning Ms. James by name, a sign of the former governor’s lingering bitterness toward her for leading what he has said was a politically tainted investigation of sexual harassment allegations against him. He has denied wrongdoing, but the inquiry led to his resignation. (Mr. Cuomo issued a second statement on Friday in which he included Ms. James’s name.)

Mr. Mamdani continued his offensive on Friday, appearing with Representative Nydia Velázquez and other Democrats at a news conference outside a federal courthouse in Manhattan to condemn what was called a “baseless indictment.”

Mr. Mamdani said the city government’s cooperation with Gov. Kathy Hochul and Ms. James would be key to fighting against federal funding cuts that Mr. Trump has threatened to carry out. He cited California, where the mayor of Los Angeles, the attorney general and the governor united to file a lawsuit against Mr. Trump’s deployment of the National Guard there.