[ You don’t have to wipe out the whole country. Just take down the eastern grid in late summer and let the riots do the rest... ]
An EMP from Iranian Nuke enchanced specifically for EMP (LOTS of Copper windings around the warhead) at an altitude of 50,000 ft or slightly more (a 777’s ceiling) right between DC and NYC would take a LOT of the east coast grid out.
Pull something like that in July or August, knock out the AC, the lights, and alarm systems after the batteries croak, and mayhem would ensue.