There is no nonnuclear EMP weapon. Every proposed EMP attack is literally a hydrogen bomb delivered via an ICBM and detonated at extremely high altitude. That is the only way to deliver one to the proper place and the only way to deliver the required energy. That’s just the physics. Even then, the actual effect at ground level, is unpredictable because of simple shielding and atmospheric turbulence. But the undetermined effects aren’t what makes an EMP fantastical. It’s fact that it’s delivered by an ICBM!
The premise of an EMP attack is that somehow the attacker could surprise their enemy and land a catastrophic knockout blow near instantaneously (where “instantaneous” is defined as “between 10 and 30 minutes” (i.e. the flight time of either an SLBM or ICBM)) with little to no retaliation. A Launch on Warning policy (i.e. launch a retaliatory strike when an incoming missile is detected in the air) along with ground and space based surveillance systems makes attempting to execute an EMP attack suicidal.
Missile launch detection systems have been operationally deployed and maintained since the 1960s. They work. Launch on Warning has been the policy of the United States since the 1960s. Implicit in a LOW policy is that the retaliatory strike order is given in minutes from a detected launch. This means the retaliatory nuclear weapons are already sent on their irreversible course before any incoming detonation occurs. This is the defense posture a hypothetical EMP attacker is lobbing an ICBM into. This isn't fantasy. This isn't just math. It’s the explicit nuclear posture of the United States for the past 60 years. It’s what makes Mutually Assured Destruction (MAD) work, and arguably has maintained peace between nuclear states for 70 years.
If an attacker has decided to launch a nuclear laden ICBM they just started a full on nuclear exchange, because that’s the response. No one is waiting to see where it goes. It’s “The missiles are flying. Hallelujah, Hallelujah.” Now. Given that you’re in an inevitable nuclear exchange, is it reasonable to waste a nuke on a roll of the dice on whether it actually do anything when you could actually blow something up? Nay! Knowing that you are being blown up?
On a related note, this is the exact situation why the proposed Prompt Global Strike weapon is suicidal. An ICBM armed with high explosives, looks exactly like an ICBM armed with nuke. Similarly, a kinetic energy hypersonic glide vehicle is not suicidal specifically because it doesn’t travel on a ballistic arc.