Most cities have deep water ports and can resupply by sea.
Regardless of deep water ports those blue cities will not get fuel. Are truckers going to risk their lives to deliver fuel? Who will defend refineries since blue states have basically outlawed refining fuel? And if blue states with ports, (Washington, Oregon, California on the west) get supplied how do they move and unload the boats? Will the democrat party terrorist antifa goons put their lives on the live protecting shipping routes when they can’t be bothered to get out of bed before noon? Just look at their “CHAZ” zone and how fast that fell apart. They can fantasize all they want about their civil war but there is zero situation they win. It will be ugly any way it happens. But they lose no matter.