Limit your searches to "Library Catalog" for books, which can be good for broad understanding and historical context. You may need to eliminate government documents by removing "United States" as an author in the Advanced Search.
This database has national and international law review articles for understanding the legal implications of a policy: its strengths and weaknesses as a law, the relationship of the law to court decisions, and the potential effects of the application of a policy.
A handbook covers the state of the research for various topics in public policy, making it a good starting place if you are new to research in that area.