Really? The problem is getting the nuclear weapon, not the delivery system. A Scud missile, available on the open market, is all you need for a vertical launch a couple of hundred miles up. At that altitude, the entire USA is covered. (Think about the Scud being concealed in a cargo container on a ship in the Gulf of Mexico, right about New Orleans. Quick setup and launch. Good night, USA.)

North Korea and Iran already have the demonstrated ability to launch a satelite into earth orbit, plenty high enough to put a bomb at the right altitude to cover the USA.

Actually, the effects would be felt at nearly the speed of light. So, if/when you see the bright light in the sky, it’s all over.

What happens is called the Compton Effect. Gamma rays from the nuclear explosion stream towards earth at the speed of light, stripping electrons from atoms in the atmosphere, which stream towards the ground. These electrons create a magnetic field which is moving along with the electrons. Electricity is created by passing a copper wire through a magnetic field, or moving a magnetic field past a copper wire.

It is estimated that hundreds of thousands of volts per meter of electric charge will be created. Plenty enough to fry the grid and anything attached to it.

Say you put your phone in a microwave, and then eventually the battery goes dead, then what?