He's warning Mamdani that the pro-genocide people will do everything they can to twist his words and paint him as hostile to Jews rather than to Israel's genocide of Palestinians. He's advising him to be more explicit about this distinction because pro-Israel propagandists are already trying to portray him as antisemitic, as they always do. He's advising Mamdani: there's an attack coming here that you need to get ahead of. He's not endorsing the attack or saying that it's justified. He's not blaming Mamdani for bringing this attack upon himself.