The MK54 suitcase nuke has the same basic bomb as the Davy Crockett.
There is a tritium component, and that would have crapped out by now.
The thing is, even if somebody took an old suitcase nuke and just set off the TNT part, you'd spread enough crap around to frighten a populace made phobic of all things nuclear by decades of environmental boogyman stories. Wouldn't even have to be measurably dangerous.
The way I see it, if terrorists had any nuclear bombs, they'd have used them by now.