Given Antifa is highly decentralized with no official leadership, what I think will happen is that anyone who calls MAGA "fascist" will be declared a supporter of Antifa and an enemy of the state, and thereby persecuted variously up to and including being disappeared entirely. So McCarthyism on steroids, basically. It will be easy to programme algorithms to sweep American citizens' social media for certain keywords. They're blatantly copying the Nazis' playbook, but the American public are too ignorant of history and what fascism even is to recognise this.