EMP has a lot of potential for years of taxpayer funded boondoggle technology. The single "definitive" event that purportedly proves that civilian infrastructure can be knocked out from a nuclear EMP is the "Hawaiian Street Light incident." A government funded study supposedly proves an EMP cause for the incident. The ones who want to gin up fear usually point to this incident from the heyday of high-altitude nuclear blasts.
Alleged Failure of Hawaiian Street Lights
On the night of July 8, 1962, the "Starfish Prime" atomic warhead was detonated over the Pacific. Residents of the Hawaiian Islands watched night turn to day from this blast that was 93 times more powerful than the one that destroyed Hiroshima. One of the U.S. Government's main purposes for the blast was to study EM (electromagnetic) effects on electrical infrastructure.
A damaging "EMP" (ElectroMagnetic Pulse) effect had been postulated since the first atomic blast in 1945, usually for long-wire infrastructure. But, no electrical infrastructure damage had been proven from any of the numerous high-altitude nuclear blasts.