I don’t know if Civil War is meant to have a clear real-world corollary for the conflict. In the movie Texas and California are aligned against the president and Florida and most of the NW states (including Idaho and Ohio) are breakaway factions that seem aligned against the federal forces as well (the implication that Idaho and Ohio are in the communist state alliance is pretty fucking laughable)
All that to say: i’m pretty sure the producers intentionally avoided real-life groups to keep the movie focused on the topic of journalism and to avoid it being used in exactly this type of political fearmongering.
Edit: also this bit in that article you linked, which seems to allude to the president possibly starting out as a liberal and becoming fascist, which is chef’s kiss
Perhaps just as controversial as the decisions of which states seceded in “Civil War” are the choices as to which states stayed. Notably, the whole Northeast, including the protagonists’ main residence of New York, has stayed loyal to the fascist government, a plot point certain to raise questions about what happened to the former liberal stronghold. In an interview with The Atlantic, Alex Garland offered up the possibility that changes in political alignments occurred as a result of the President’s own politics changing between his first term and his third: “He may be a fascist at the point we meet him, but he presumably in his first term didn’t say [that] …”