It is clear that they see Trump as deeply representative of their priorities and likely to stand behind them no matter what. Unfortunately, this makes clear what their priorities are. Police unions have decided that their first and foremost principle is to protect individual officers from any form of accountability, up to and including for rape and murder; they apparently have also decided to include white supremacy in their formal charter.
If you combine this with other police union statements in the past few days - like the Miami union's saying that they will not provide police protection to the Dolphins football team until and unless the team forces its members to stand during the anthem - it has become painfully clear that police unions across the country have converged on a belief that any opposition to them, any suggestion that their power should be less than unlimited, is "anti-cop."
I have always been suspicious of the notion of public sector unions, but police unions have gone so far beyond any prospective worst case of how such a union could behave that their very existence has become unconscionable. The armed forces of a state must always be subordinate to civilian oversight - and a police union which can demand exemption from this, and threaten violence or public disorder (as Miami's just did, and as many others have) if it is not granted, is an enemy of democracy itself.