From a foe say China Russian Iran NK et al, or from within? If it were due to a China EMP attack China would cease to exist I would think. As would most all nations with hostile intentions towards the USA. Too many USA military assets and the really big bad stuff deployed at sea in the air and and in the ground world wide for the instigator to survive. Now having said that the planners the lucky the ruthless and the willing to kill first will last longest but no guarantee on true long term societal survival The sick the elderly the government program addicted people will die out first. The vast masses the lower 48 would not do well in a true worst case scenario and it occurring is not the least bit out of the questions. If the grid down scenario is from within I don't have a clue, Personally for that to occur I say it has to be a military involvement scenario. I can only guess & think I know what I hope I would, do but that is all.