“Because it would take an enormously powerful EMP to take out a significant portion of the power grid. “
a 1-kiloton blast can create an EMP almost as strong as a 100-kiloton blast. That creates a vast area of the atmosphere when exposed to gamma rays that emits a brief but powerful RF pulse. Because the atmosphere for thousands of mile around (for a sufficiently high nuclear detonation) is effectively an “antenna” everything underneath is effectively in the “near field” where fields do not decay exponentially - but decay linearly.
Your conclusion is incorrect.
How strong of a magnetic pulse would a 1-kiloton blast create? And what and how would it damage the power grid? Not assuming you know or should know the answer...just wondering. It seems to me that the pulse would be of the transverse type. If so, would not the radiation decay at a rate inversely proportional to the radius? In which case a pulse high up in the atmosphere would decay immensely before it hit the earth...unless it was somehow guided to vulnerable infrastructure.