It isn’t sheriffs or police chiefs doing this on their own. Individual counties are changing the law within their counties to say you can’t refuse a blood test.
I don’t know how it will stand up in a state court. I’m not familiar enough with the relevant portions of the state constitution to say that they can’t do it at the county or city level. I would hope they can’t.
Sounds like the counties are doing the “legal ‘till we can’t get away with being illegal any more” or the legal equivalent of it is easier to ask forgiveness instead of permission.
local governments hate preemption.