What a maroon. OF COURSE every enemy who desires you dead is a threat to your existence! Their relative ability to inflict it can change in a moment. The treat of a muzzie whacko with a box cutter in Boston was small threat to the "A" ring at the Pentagon, until that place and time made them a huge one. But the threat was ALWAYS there and ALWAYS prosecuted to the extent the extremist could.
So at which point would Professor Bell prefer to deal with it at: arrest them for visa violation in 2000, or try to wrest control of the airplane from them two minutes before they crashed it?
I think Prof. Bell would prefer to hold nuclear arms "talks" with Iran....