In 2020, Jacob Rubel, who was then my advisee as a Tufts undergrad, launched with the lead author Mathis Ebbinghaus a project to assess the policy impact of Black Lives Matter protests. He got support from another advisee of mine, Jane Romp, and two other Tufts undergrads to hand-collect data on police budgets and political processes in 264 US cities (all of the 300 largest cities for which data were available), and he collaborated with Mathis Ebbinghaus and Nathan Bailey on the analysis. The results are now published as:

Mathis Ebbinghaus, Nathan Bailey, Jacob Rubel, “The Effect of the 2020 Black Lives Matter Protests on Police Budgets: How ‘Defund the Police’ Sparked Political Backlash, “Social Problems, 2024;, spae004, https://doi.org/10.1093/socpro/spae004

Overall, funding for police did not change to a statistically significant degree from 2019-2021. Larger protests accompanied increases in police budgets, but not to a statistically significant level (hence that relationship could be noise). However, in cities where Republican voters were more numerous, larger protests were associated with increases in police budgets. The authors consider the timing of elections and show that this backlash was not a result of electoral pressures. Rather, cities with more Republican voters seem already to have had more conservative (or pro-police) political cultures, and those city leaders reacted to BLM protests by increasing funds for police.

See also: police discrimination, race, and community poverty; on the phrase: Abolish the police!; who protested in 2020? how change is made