I read somewhere that at some point the prevailing culture in American Police forces changed from putting public safety first to putting police safety first.

Not just in America, in the UK the Health and Safety culture has resulted in drownings where rescue personnel refused to enter ponds to assist victims. And currently an enquiry into the London Bridge attack has heard of how paramedics, thinking of their own safety, refused to help patients for up to 90 minutes after the attackers had been killed.

The US police increasingly resemble a paramilitary type operation with swat teams and armoured vehicles, all predicated on the protection of officers.

It was probably inevitable in a country where even automatic assault weapons are freely available.