EMP would probably cover the entire US.
No, there are published papers from Sandia and Lawrence/Livermore that even if every single SS-18 Satan had the Mod 3 warhead (25MT) all launched and detonated at EMP altitude, it still wouldn't cover all of CONUS or have long lasting effects. I forget the yield, but for ONE nuclear warhead to cause catastrophic EMP damage over all of CONUS would be in the gigaton range or high hundred megaton. Every nuclear weapon (less SADM/tactical nukes) the Russians have is approx. 1,056GT.
The SS18s with the 25MT warheads were strictly for destroying the LCCs outside of Warren, Malstrom, and Minot AFBs, plus Site R, Mount Weather, Greenbriar Hotel (now untargeted), NORAD, Camp David, White House Bunker, Pentagon bunker, and Naval Observatory Bunker.