Heck, something like this can happen with a large solar flare. If anything we all should assume not if it will happen but when.
I have always read that it wouldn’t be (relatively) that expensive to harden against this. Why isn’t it being done?
Solar flare EMP can take down some the power grid but a nuclear EMP will destroy not only that but most of all electronic devices. Can you imagine the suicide rate in the country once folks realize their smart phones are dead forever?