It depends on what anyone means by "Civil War". There's no neatly defined pair of geographical and political blocs here, ready to face off against each in the manner of the Union and the Confederacy. It's also not as though there's a coherent single leadership to lead that kind of conflict. Trump can barely work his TiVo on his own let alone listen to anyone who isn't him talking for any length of time, so it's not like he's going to mount any coherent effort to fight a war.
That leaves his base, who are dangerous in a far more abstract way. Terrorism, shooting, mass unrest? All entirely possible, but fragmented and as incoherent as their figurehead.
So Civil War, in the conventional, literal sense? I doubt it. A perpetual, low-grade conflict ignited and sustained by individual deluded idiots (or in small groups) with guns, Internet access, and an inflated opinion of their capabilities? Sure.