Forget the military threat, imagine the chaos a person could cause with a few thousand dollars worth of shape charge drones if they wanted to, for example, disable a national power grid. Large substation transformers have lead times measured in years. It would cost a few hundred bucks to destroy one. I imagine a guy in a box truck doing a tour of the US, dropping a shape charge drone or two with cellular data connections outside 30 or 40 major substations and activating them all at once.
Once the grid goes dark we're going to suddenly find out that black start of an entire electrical grid is a very difficult thing to do.