Well, "nuclear suitcase bombs" are usually envisioned as taking out a city. Wheel one into Times Square, push the button, and boom, millions dead. The Davy Crockett's yield was about 20 tons, so it would be like a really big truck bomb going off. Not a good thing to happen in a crowded city, but we're talking about a couple of city blocks being destroyed. For a sneak attack, you'd probably be better off buying or stealing a tractor trailer and loading it to the gills with ammonium nitrate.
