I would say this...based on having done a fair amount of reading on EMP over the past thirty years....when all the fools were sitting there and worried about opening up the nuke science and crying over nuclear weapons...the real absolute threat was that one day....someone would use EMP to take down a civilized nation.
Once everyone realizes the impact and power of EMP....I think it’d be a primary weapon of most terrorist groups from that point on. You could target just California and probably take down enough of the nation’s economic strength...that it’d take six to eight years to recover just from a very limited and isolated use.
I’d also suggest that Iran would find some nation very friendly to it....helping to retaliate immediately against Israel, and bring it to the Stone Age within weeks.
Ever heard of a faraday cage? A car is a faraday cage. So is a metal building.