At issue is the federal government's so-called 1033 Program, which permits the Pentagon to give military hardware to local police departments. 

In a June investigative report, the New York Times documented how that program, among others, has allowed police departments to "receive tens of thousands of machine guns; nearly 200,000 ammunition magazines; thousands of pieces of camouflage and night-vision equipment; and hundreds of silencers, armored cars and aircraft." Newsweek notes that the program originally started in 1990 as part of the so-called War on Drugs, the idea being "that if the U.S. wanted its police to act like drug warriors, it should equip them like warriors, which it has ? to the tune of around $4.3 billion in equipment."