North Hollywood Shootout (1997) – A tipping point in police militarization

Or further back in time. "Another reason for the creation of SWAT teams was the fear of lone or barricaded gunmen who might outperform police in a shootout, as happened in Austin with Charles Whitman." - https://en.wikipedia.org/wiki/SWAT

It's a series of step functions, ratcheting up the police to handle new worst-case scenarios. And training them to think that anything can be a new worst-case scenarios. Like selling lose cigarettes or potentially using a fake $20.