Active Army 1981-2005. I imagine that units would obey initial orders to "assist law enforcement in taking down powerful terrorist cells." Once it became clear that the "terrorists" were actually the law-abiding mass of the American citizenry, however, units would cease to obey such orders--as a minimum. If pushed any further at that point, the chain of command and the bonds of discipline would dissolve. The US military, as an institution, would not obey such clearly unconstitutional orders.