See: http://polisci.osu.edu/faculty/jmueller/APSACHGO.PDF
ABSTRACT: A terrorist atomic bomb is commonly held to be the single most serious threat to the national security of the United States. Assessed in appropriate context, that could actually be seen to be a rather cheering conclusion because the likelihood that a terrorist group will come up with an atomic bomb seems to be vanishingly small. Moreover, the degree to which al-Qaeda--the chief demon group and one of the few terrorist groups to see value in striking the United States--has sought, or is capable of, obtaining such a weapon seems to have been substantially exaggerated.
