Good Point, Bassomatic.  There are actually 3 separate "Grids" in the U.S. as far as major grids are concerned, but the point is still well taken.  The gas pipeline ransom currently happening makes that point clear as to how much damage could be done.

Perhaps, in the long run and in the far distant future, this Achilles Heel won't be such a vulnerable point for the U.S.  Of course there could be major improvements in cyber security that would ameliorate the current risk, but in addition maybe we will see a significant move toward neighborhood grids and microgrids as part of the solution to the problem.