The SA-2 has a 300 pound warhead. We had atomic bombs one third the size in the ‘60’s. Something similar launched from the coasts would do a very good job on the US with EMP. It would no t have to hit Omaha. Nevada and Ohio would do just fine.
As I stated, the enemy has much more suitable delivery methods than an SA-2. There is no logical reason they wouldn’t (or couldn’t) employ them instead.