Often.
The militarization of law enforcement agencies from the rural SWAT squads up the the feds is very troubling, and will contiue to have ominous and far reaching unintended consequences...
A cop was clearing out looters from stores, backed up by several National Guard troops. The cop said "cover me, I'm going in." When a cop says that, he expects his partners to observe the situation and be ready to shoot. The troops, being trained differently, began suppressive cover fire. The cop was rather, er, dismayed.