There's a good chance the first nuclear strike on American soil will be delivered via common carrier from an unidentifiable shipper. So who do we totally destroy? Federal Express maybe?
I would bet that whatever group that managed to plan, deliver and execute a plan against American interests, will not be able to contain their shear joy. In fact the main problem with an attack is not finding someone to take credit for it, but to sift out the one that actually did from the inflated number of groups claiming they did it.