It is too soon to tell what motivated this, although the bomb was poorly designed, suggesting poorly trained individuals. What does this event mean? Again, too soon to tell, but I am surprised it has not happened before. The only thing that I can predict is that the Republicans will blame Obama for the event.
One other thing--it does point out that cities that get rid of their street vendors do so at some peril. These guys provide an additional set of eyes on the street.
[UPDATED] Good, clear discussion by someone, Steven Coll, who knows more about this stuff than I.
The description of the Dr. Seuss-inspired contraption in the back of the S.U.V. offered by the police suggests someone who tried to go to school on the Internet but didn’t have the patience to complete too many classes.