The police really cannot back down on this, or literally, more police will die. Any other union that opposes the police and supports de Blazio is going to sour police on them as well. Playing nice means nothing when your people are dying.
The bottom line is de Blazio is just one guy, and there are lot just as “progressive” as him, but without hating the police, and who are not going to create a civil war in the city.
My sympathies are with all police officers doing their jobs. Let these liberal bastions eat their own.
De Blasio is in exactly the same position.
"Progressive" leaders cannot survive without obedient security forces. The police union has demonstrated that the forces under their control are no longer reliably obedient to the elected political leader.
Neither side can survive if the other side remains in power.
This cannot end well - for participants or spectators.