It is also not known how American society in general would react if massive infrastructure failures occur over a large region and for a long time.

"The Early-Time (E1) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid"

Sections of interest:

• 7.2 Susceptibility of Power System Equipment
• Table 7-2. Some previous studies of the response of the power grid to E1 HEMP

  One of the referenced studies: [ORNL HEMP Assessment Program ](http://www.ed-thelen.org/pics/EPRI-HEMP-2017.pdf)
  

Seems like most of the power grid vulnerability comes not from the power systems themselves (transformers etc.), but from the associated control systems.

it can be seen that the “brains” and communication systems of any modern power facility could be vulnerable to E1 HEMP

Fun:

In this case we heard a “bang” associated with the damage, and further testing showed that a resistor on the circuit board was blown up

• Table 7-8. Fast pulse results for a typical PC and network switch
• Section 8: Impacts on Society of E1 HEMP Power System Failures
• Appendix: E1 HEMP Myths
  • Important note: it doesn't seem like personal electronics will likely be affected (though, as the authors qualify, it's always possible).