“An electromagnetic pulse (EMP) attack poses a direct threat to the U.S. electric grid—a threat that is poorly understood and lacks the leadership to address it. An EMP—a high-intensity burst of energy caused by a rapid acceleration of charged particles from either solar weather or a nuclear bomb detonated high in the atmosphere—can cause devastating damage to the U.S. electric grid, and severely impede recovery.”
Source: The Danger of EMP Requires Innovative and Strategic Action | The Heritage Foundation