I called this right after 9/11:
Intelligence and covert operations are the first line of active defense and the first echelon of attack. The aerial suicide attacks on our people and the symbols of our power took enormous amounts of time to carry out. This is one weakness of our enemy. While they may carry out small attacks using small arms or small bombs at a moment's notice, truly horrific attacks require time because they must be planned in the shadows to avoid detection.
We have stopped the big plots in America so far. The small plots or just "jihadi rage" spontaneous attacks, extending to using just vehicles, too, is bad enough but not as bad as it could be if the big plots were easier to carry out.
But it is difficult to stop because you don't need to hear "dog whistles" covertly sent by Islamists to know that they want you to radicalize and kill infidels in the name of their version of Islam. They just aren't shy about their intent.
Helping Islam win their civil war to define Islam for a modern world and reject and marginalize the jihadi ideology is the only way to really crush the lone wolf-type attacks.