This was phase one in the militarization of America’s police forces, as described in Radley Balko’s essential 2013 book on the subject, “The Rise of the Warrior Cop.” Phase two, in which the federal government began supplying local police with military hardware, began in the 1990s and accelerated after 9/11, under the theory that Islamic terrorists could strike anywhere, and that it might take a cop with a grenade launcher to stop them.

In the name of local preparedness, Washington has been bestowing antiterror grants and Pentagon surplus on communities barely touched by major crime, let alone by terrorism. Tanks and aircraft, helmets and armor, guns and grenade launchers have flowed to police departments from Des Moines (home of two $180,000 bomb-disarming robots) to Keene, N.H. (population 23,000, murder rate infinitesimal and the proud custodian of an armored BearCat).

Last week, The New Republic’s Alec MacGillis ran the numbers for Missouri and found that the state’s Department of Public Safety received about $69 million from the Department of Homeland Security in the past five years alone. Which helps explain why the streets of a St. Louis suburb flooded so quickly with cops in gas masks and camouflage, driving armored cars and brandishing rifles like an occupying army. It’s our antiterror policies made manifest, our tax dollars at work.

And it’s a path to potential disaster, for cops and citizens alike. The “S” in SWAT was there for a reason: Militarized tactics that are potentially useful in specialized circumstances — like firefights with suicidal terrorist groups — can be counterproductive when employed for crowd-control purposes by rank-and-file cops. (The only recent calm on Ferguson’s streets came after state cops started walking through the crowds in blue uniforms, behaving like police instead of storm troopers.)

To many critics of police militarization, of course, the helmets and heavy weaponry are just symptoms. The disease is the entire range of aggressive police tactics (from no-knock raids to stop-and-frisk), the racial disparities they help perpetuate and our society’s drug laws and extraordinary incarceration rate.