What comes from the sun is but one component. What comes from a nuclear weapon adds another factor to the mix that the sun doesn’t even touch. Protecting against only a CME will not harden the grid against a high altitude nuclear weapon. And a cyber attack will NOT do the same damage as either one of the other two.
"Ye hear of wars in far countries, and you say that there will soon be great wars in far countries, but ye know not the hearts of men in your own land."