I, myself, am a serious techtard in every way, as well as being a high school kickout/dropout. I only can slightly grasp what my betters say in this regard.
I am given to understand that the effects are rather localized and not continent wide, but it may be dependent on factors that are definitely way beyond my ken.
Depending on how parts of the grid go down, the initial attack might not get everything, but the ...shall we say, “less than graceful” failure of parts of the grid might lead to cascading failures.