Without knowing any of the details of how our power grid is structured, what I would like to suggest is that even if we cannot protect every discrete part of it, what we can perhaps create is firewalls, sections of the grid where perhaps power moves more slowly by design, such that there would be sufficient time for a circuit breaker of some sort to pop in a condition of overcurrent. We could perhaps, with relatively less effort than a comprehensive, honest solution, create sections of power, sections of flow, which are severable, such that if an attack hits one part of the country, it is limited to that region. And of course the more segmented we can make it, the better. I would in fact draw an analogy between physical power, and the limitations and firewalls of political power which our Founders wisely wrote into the Constitution.
I am inclined to say that war with North Korea would be stupid until we can do this. That we can win the war, and do so quickly, is indisputable. That they could inflict vast harm even on mainland America in the process is a possibility we need to consider carefully.