[chrisser]

"Perhaps the most likely threat is from a suitcase nuclear weapon in a rusty car on a dock in New York City,"

If it's in a rusty car, it doesn't need to be as small as a suitcase - trunk-sized would do nicely.

If you expand "car" to include "light truck", and especially vans, then you can effectively hide a much larger device than a suitcase.

[meatloaf]

And if you conceal one on a ship during a yard period unknown to the crew except for one, maybe two? Certainly a dockside crane could lift more than 200 lbs or 2,000 lbs.