A 150 KT device is quite large and unlikely, but an attack involving smaller "mini-nukes" (~ 5KT or less) is very likely in the next 10 years or so ... my guess sometime around 2013 +/- a couple of years either way.

Mini-nukes physically are not enough to take out a decent city, but tend to be very messy in regards to radiation; larger nukes tend to be "cleaner" relative to their power due to being more efficient.

Digressing a bit, but point is that terror attacks involve nukes are very likely - I for one am surprised such an attack hasn't happened anywhere in the world yet ... one can chalk that up to skill of various law enforcement/spy agencies and in very large part plain 'ol luck.

As far as where the attack would originate from ... a person(s) from the middle east is the most obvious, but an attack from an American(s) is just as likely - the Oklahoma bombing in '95 illustrated that attacks can come from anywhere; some have speculated that the attackers had support from middle easterners - even so, the actual attackers were American.

In regards to the TV ad, I personally feel it's not helpful since the real threat is everywhere - and the solution is the U.S. government respecting the rights of the people, and just importantly NOT developing mini-nukes, since some of them will very likely eventually be used against us by terrorists.

Ron