A meditation on an individual right that used to be treasured by the political left at least as much as the political right.
Of course, the Second Amendment doesn't only protect an individual right: it also protects the right to organize as militia. That may be the part we're missing in this discussion, both as applies to resisting armed tyrannical units -- the Waffen SS were a paramilitary, not a military force -- and as applies to a more coherent defense against active shooters. The citizen as officer of the state should be armed, trained, but also integrated as a potential actor into the official planning for responses. Much can be done by teaching citizens not only how to use a firearm to defend themselves and their immediate space, but how to link up and work together in the face of a common threat.