My belief is that it would be skirmish based, if it would happen at all. Proper battle lines won’t be drawn. Strongholds might exist within cities/towns.
I believe militias would act of their own accord but operate within a wider network.
Trump wants/ed to antifa to be the wider network, and his rhetoric has been a successful to a degree.
I think active military would be deployed more for deterrence of full on violence than acting on behalf on one side, however shyt could pop off, if active men take up sides with one group.