See https://chris-said.io/2020/06/18/everything-ive-learned-abou...
Regardless of which side you believe, it is clear that any "worst case scenario" should include the possibility of an EMP attack that actually does take out the power grid.
Things are setup to fail safe which preserves equipment but defaults to turning everything off. Getting significant parts of the grid up again should take days even if your stuck with rolling blackouts for years.
Further, EMP isn’t a magic wand that instantly destroys all electronics, there is a huge range of sensitivity not just based on type of equipment but also if it’s running and the orientation it’s in. Taking out farm equipment that’s off is really difficult. The actual nukes are a much larger threat.
(and it should be further noted that this conclusion was that the US carrying capacity for life would decrease to 30m sustained by like subsistence agriculture. I expect that those deaths of hundreds of millions would be over decades, not quickly, and I really really doubt that we'd be unable to recover more than some of our agricultural capacity in a decade)