David,

I don't think 'lone wolf', "jihadist-inspired terrorism' or 'mass killing' are at all mutually exclusive. It can be all three at once. I think this is the future of terrorism in the United States - right, left, Islamic, or other.

1. Mass communications and social media enables passive connectivity between sources of radicalization and would-be radicals. A 'network' exists insofar that ideological infrastructure is constructed - traditional methods of underground activities are far more risky and no longer necessary. Any wannabe terrorist can find inspiration - and direction - online.

2. The easy accessibility of guns means that any would be radical can inflict mass casualties on soft targets. Guns are (1) easy to acquire, (2) easy to use, and (3) difficult to detect. They can be purchased without arousing investigative interest. And when it comes to reliability, guns perform at a far higher level than IEDs. The threshold for action is far lower with guns than with any other weapon.