You make a compelling case. One could argue that the puzzle pieces are being aligned for such a possibility.
The major pieces, the military and DHS/TSA are in place and aligned. I seriously doubt American troops would fire on American citizens, so an order not to fire on city mobs would not present a moral problem. I believe, maybe incorrectly, that most people who go into the military do it primarily for patriotic reasons. The DHS/TSA types are completely different. I believe they do it for the money and power trip. They would not hesitate to knockdown doors and search residences while holding citizens at gun point. I think Boston and TSA behavior in general has proved that.