Fictional EMPs over the US scenarios never seem to take into account support from non affected allies. Fuel, generators, food, other supplies would pour in.
There are studies do take that into account.
3 air bursts could take out every electrical circuit and wire in the continental US. The following are shut down: water, waste, food transportation, refrigeration (for food and medicines), pumps, lights, all transportation except walking and bikes.
The average 300,000 people in flight over US would die right then. Lack of water would start killing lots of people within 1-2 weeks. People needing insulin or some other drugs to survive would die. Within a month, you would get into food scarcity and probably lots of murdering. Beyond that, starvation and some disease (from bad sanitation). If it's winter, a bunch of people would freeze to death.
This is for 300 million people over 3 million square miles. No nation is quickly going to get water and food and medicine to that many people over that much area. External supply and logistics for that are larger than anything done in history by orders of magnitude. Canada and Mexico wouldn't be able to help, as part of their stuff would be ruined as well. They'd have their own deadly problems to deal with.
You aren't going to use any existing wire or pump or electrical device. They are all ruined. You can plop down a generator and then run some cables from it, and the extent of those cables is the extent of your power. You want to pump something? You'll be installing a new pump. You want a control system on a pipeline or something? You'll be installing a new one, along with all new wiring. You want refrigeration? You are bringing it with you.
An emp attack on the US would be horrific. Estimates from studies are 90% of Americans would die withing 1 year, even with foreign help.
Yet, it would take only $20B or so to help reduce casualties a lot. Basically some redundant transformers, wire, and other stuff in Faraday cages, and some hardening of some things. $20B is 0.3% of the annual gov spend. It is the cost of buying 10 B-2 bombers.
But population doesn't really know or care.