With EMP, a nuclear Iran and already-nuclear North Korea would possess abundant assured destruction capability against America. To deter them, does it make sense for the U.S. to rely on a retaliatory threat of immediately killing perhaps 1/3 of their much smaller populations (Iran: ~84 million; North Korea: ~26 million), destroying much of their relatively meager industries? The answer is NO! Kill 2/3 instead? Still NO!
To illustrate, Iran’s mullahs could decide it is worth accepting the favorable MAD death ratio (possibly as high as 10 U.S. deaths for 1 Iranian death, or 10:1) of an EMP attack to destroy the Great Satan. On the world stage, Iran could deny the attack by shifting blame, such as to a secret U.S. space-defense weapon that went awry or to terrorism. A U.S. response would likely not be immediate as various leaders argue in Washington, D.C., and nations debate in the United Nations, where Russia and China would support Iran.
Stressful or disastrous outcomes could follow. For example, Russia, China, or both could offer Iran protection by threatening massive nuclear attacks on an already suffering America. Suppose the U.S. did eventually retaliate against Iran. In that case, Russia, China, or both could decide to finish off a much weakened America, possibly by starting with more EMP attacks to destroy feeble recovery efforts. With EMP-damaged electronics, prolonged national power outages, and already having expended part of its arsenal on Iran, a U.S. response to Russian-Chinese attacks could be fragmented and much less effective than before Iran’s EMP attack.
Similar discussions would apply to North Korea, except that North Korea’s MAD death ratio relative to America could be on the order of 30:1 for an EMP attack. With one or a few nuclear weapons and delivery mechanisms, small nations and tiny terrorist organizations can gain tremendous leverage over MAD-obsessed large nations!