"Improvised Nuclear Device - IND".....
Fresh Report - came out the day before the shutdown. There really is no such thing as an improvised nuclear device, its a somewhat recently coined DHS term. The term is basically referencing a poorly engineered device & or a poorly constructed device that ends up with a much lower detonation yield & or results in a tremendous amount of fallout.
New York, BWI/DC, Chicago, & Houston would most likely be the target(s) of preference.
Timing is strange, go read all 68 pages or so if you'd like.
http://cryptome.org/2013/09/gao-13-736.pdf