I remember defund the police narratives. However despite these defund the police talks the majority of police budgets in the US continue to rise the last few years.
The performance of police, like of most professions, is highly impacted by morale. The defund narrative painted police work as inherently racist and oppressive, which obviously effected morale.
Defund the police came out of specific incidents, normally resulting in deaths, which are now being covered by police body cams and filming. From my own perspective the morale being affected is tied to the usually narratives of what happened in the incidents no longer being backed up by what the camera shows. Defund is the wrong word in my opinion though - if this was another professional job it would be more police training. We shouldn’t see indigents of a traffic stop resulting in the death of a driver with multiple police involved. Or why can I ask someone who lives in the woods come up with multiple names of people killed by the police that were unarmed - I’m sorry the morale is down and that it affects job performance but it can’t be that we expect to have multiple unarmed people killed a year as a normal part of the job.
I don’t have any specific data, but it seems intuitive and cops themselves are talking about it. https://www.npr.org/2021/06/24/1009578809/cops-say-low-moral... and a bit here https://www.manhattan-institute.org/verbruggen-depolicing-al...