Not to tempt fate (I laughed at "World's Dumbest Terrorist" headline following the WTC attack in '93--I've regretted it for 10 years) but what's the next rung up the ladder?
A very smart, extremely well-read (he read Herodotus to relax) friend of mine explained to me how the 'suitcase nuke' is the stuff of fiction and any other nuclear device too big, too technical, and too expensive to be entrusted to 'subcontractors' like al-Qaeda. So what's left?
Personally I’m more concerned about cities other than NY.