Al Qaeda central is not the driving force of terrorism as an operational machine but rather its ideology serves as an inspiration for self-organizing local groups to carry out their own attacks.
But other experts, including Bruce Hoffman, maintain that it is established organizations like Al Qaeda that remain the dominant threat and that we must focus more on the organization and its capabilities rather than random, radicalized individuals.
The pattern of terrorism arrests since 9/11 seems to support the argument that homegrown radicalism is the greatest threat the United States faces and that Al Qaeda has lost its capability to carry out direct attacks outside of its Afghanistan-Pakistan operating base.
But just because homegrown plots constitute the majority of those uncovered doesn’t mean that homegrown terrorism is the greatest threat. Many of the homegrown plots have been all talk and little action.
Even if the plots were executed, they would have been limited in scope - small explosive and ambush attacks or targeted killings. Mehana allegedly plotted to ambush and shoot shoppers at a mall. While it would have been a tragic incident, it would be nowhere near the scale of 9/11 or the Mumbai attacks.
In addition, there is a significant difference between self-taught would-be terrorists and stealth operators who have had training and contacts overseas like the sophisticated Mumbai attackers, Ramzi Yousef, or Mohamed Atta.
Lydia Khalil, a former counterterrorism analyst for the New York Police Depatment, is a fellow at the Council on Foreign Relations.