Protesters should try and be kind to the police. We might need the police, as well as other lower level civil servants, to disobey crazy orders that could come down from the top. The top being Trump Administration, Congress, and eventually Republicans on The Supreme Court. We might need our mid level government workers to maintain common sense. These people can help us; especially if we don't alienate them.
A few weeks back, I heard that some mid level military folks were saying that they were ready to disobey illegal orders (about torture and so forth) that might come from "the commander in chief." They might have to disobey orders that violate Geneva Conventions; for instance.