This is an excerpt from a US Gov't Report called "The Effects of Nuclear War" published by the Office of Technology Assessment, released May 1979.
I think it's important to know the science behind this potential scenario rather than the hollywood speculation. From this report, it seems, while catastrophic, a so-called "suitcase nuke" would hardly cause the destruction of an entire city, but rather maybe only a neighborhood.
Of course the Gov't doesn't advertise this knowledge in order to keep us all in fear. So fear less people! Odds are terrorists won't be the one to destroy america, but keep an eye on yr local politicians, they can do it far easier and don't need no nukes, just lawyers, cops, zoning commissions, eminent domain, and real estate developers.
(click to enlarge)