After working in a test lab that tested mechanical and electrical components for some military contractors; most electronics used in the military are not protected against an EMP. In fact the mil requirement for most produced items withstanding and EMP was dropped almost 20 years ago.
ESD (electro-static-discharge) is minor version of an EMP.
Visualize a static shock from the carpet when you touch someone and they say ouch.
You body can store between 4,000-35,000 Volts as a capacitor your body can store up to 100 picofarads
As an ESD this can destroy most electronics that are not protected.
EMP's can knock out major and minor electronics including a power grid over 1000 miles a way.
(Starfish Prime 1962- with a small yield)
Static charges break down at 10,000V/cm. EMP's can actually generate a continued and growing ESD as they travel.... south, but not north towards the magnetic pole.
An EMP or nuke denated for an EMP over say North Dakota (because EMP's travel mostly south) would knock out most electronics of 90-95% of the country. A EMP detination in Florida would affect nearby states and the northeast, central and west coast would be unaffected.
Now the question is what can you do to protect yourself?
A Faraday Cage will protect electronics. Tin foil wrap (not aluminum foil) will work. Ferrous metal containers will protect electronics. That means metal gun lockers and safes will save your electronic sites.
The mil dropped its requirement for electronic hardening because the cost out weighted the benefits of a possible EMP. IMHO you have bigger things to worry about like food and water shortages in a SHTF scenario. If you think you might ever encounter this think about a BUIS. Personally all of my SHTF guns have iron sites and nothing attached to them that will break or fall off. K.I.S.S.- The ultimate in reliability.