Adrienne LaFrance's piece in The Atlantic is titled "The New Anarchy." Pull quote:
The form of extremism we face is a new phase of domestic terror, one characterized by radicalized individuals with shape-shifting ideologies willing to kill their political enemies.
But then LaFrance directly references a previous iteration of exactly that: "Propaganda of the deed." For some reason she attributes the idea to one of its later advocates, Luigi Galleani.
She doesn't reference later improvements to that doctrine, such as Amoss's "leaderless resistance" ideas.
And she only references social media with respect to the fact that "conspiracy theories now spread instantly and globally," rather than addressing how it facilitates both open and predisposition-coded calls to action, making it easier to informally coordinate leaderless resistance, or to inspire propaganda of the deed.
The social media aspect is really the only new thing here. "Radicalized individuals with shape-shifting political ideologies willing to kill their political enemies" have been around forever, and their tactical approach has been evolving for at least a century and a half.