Terrorist organizations like ISIS have encouraged sharia-supremacist Muslims to attack in place — i.e., where they live in the West — rather than come to Syria. We are thus seeing more of these ad hoc strikes that require little or no expertise to pull off. In the Nineties, we used to be ironically relieved that the jihadists always wanted to go for the big bang; 9/11-type attacks are horrific, but they are extremely tough to pull off, and there are usually opportunities (as there were with 9/11) to disrupt them. That’s why they so rarely succeed. We worried that someday it would dawn on these monsters that there is a great deal of low-hanging fruit out there (virtually indefensible targets, like subways and crowded streets) that would be easy to attack, almost no preparation or coordination required.
Now, they’re going for the low-hanging fruit.
In terms of what the wonks like to call the “threat mosaic,” we are now in straits more dangerous than ever. We have highly trained, competent jihadists who are capable of pulling off sophisticated strikes that could kill hundreds or thousands at once; and we have motivated would-be jihadists who have been encouraged to do the kind of crude attacks that are within their limited capabilities. The crude attacks, we are learning, are just as effective at stoking an atmosphere of intimidation as long as they happen with some regularity.