ACAB

Seriously. He could not have disengaged more gently. This is the straight up murder I mention every so often.

So, they shot because they were fearing for their safety?

And they shot from behind the car, through the back window, while the car was driving away from both of them.
Okay.

What was the threat they were trying to stay from?

Right after the article mentions their rules of engagement in that situation being that they should have backed away from the moving car, it then states that the action would likely be considered justified due to the officer being in danger.... from choosing to hold on to the moving car? Like his injuries are clearly because he didn't let go of the car until it was going fast enough that he fell off and skidded... that seems like his choice and not something the driver did.

They are not authorised or recommended to use force to prevent a "suspect" from fleeing.

where’s all these second amendment defenders to save the day?

Oh, more USA gov agencies now on at-will public executions.

They are trying to kill/privatise the Post Office bcs they don't wanna do that prob.