With Homeland Security research, often you have to start researching in order to know what you need to research.
Grab a sheet of paper or the attached Keyword handout, start searching the big picture -- the broad -- topics to learn more.
As your search, jot down specific terms you learn, relevant laws and Executive orders, any applicable amendments and court cases, and even specific researchers whose names seem to come up more than once.
Once you know more about your topic and now have some specific keywords, try some new searches using those terms and ideas. And think through your searching and try to be specific with some strategies.