Well, Obama did say at the outset of his presidency that he wanted to have a domestic armed force to counteract any “violent terrorist acts” that might occur. Almost every federal agency and department employs an armed enforcement division, which by now may number over 200,000 armed personnel with arrest powers. Your comment on the oath to “Protect and Defend the Constitution” is a good one; In addition, Obama is on a path to Federalize the entire LE structure in the US. I know a lot of local police departments with some pretty sophisticated hardware; they look a lot like a military unit.
True that.
But where local LE differ from military is that the citizenry is a lot more likely to be close to and know where the families of the LE are. That's a lot different than an anonymous soldier brought in from somewhere else.
Also, I wonder what the resupply capabilities of a town's police would be if chaos erupted on a large scale. They might find themselves running low on consumables fairly quickly. They don't have the supply lines the military has.