I actually beleive this will happen someday, maybe next month, maybe 5 years from now or somewhere in between.
Hard to imagine how life will change here in the US if we go thru a multi-year period were 2-3-4-5-10 suicide bombers kill themselves (and crowds of others) everyday for months on end like goes on in Iraq.
Not sure the American psyche is upto living like that...though other countries seem to go about their lives as best they can (i.e. Israel).
Hope I am wrong, but I also happen to beleive that it is inevitable that someday in my lifetime (another 50 years maybe), a Nuke will go off in a city in the US...hard to believe that we could prevent it if an enemy was well-financed and determined enough...
...security forces are currently on top of the situation, but we have to be lucky everytime. The enemy only has to be lucky once.