If I'm wrong, let some nuke experts correct me. Plus, if suitcase nukes were so available, why don't you think the black market arms dealers s have not provided Iran or other rogue nations with them? Many went missing after the fall of the USSR. They take a lot of maintenance to remain viable.
Bottom line: They all know about our Tridents and the USA is the only nation to ever use nuclear weapons, and we would do it again. Sleep in peace, and thank our submariners on those subs.
I simply dont believe, suffering from the effects of an EMP attack, wed have the ability to find the remnants of a scud delivered nuke somewhere over thousands and thousands of square miles of middle America. I will also need more than your assurances that we have the ability to identify a nuke from, say early 60s Soviet Union or a renegade construct. Regardless, if some ISIS type group launched it, what would they care how we retaliated. Scuds are easily available, a non descript freighter in the gulf with a scud is easily done. Dont fool yourself in believing that nukes or the material to construct one arent available. I envy your ability to whistle past the graveyard on this.