If you're interested in a broad topic in Politics & Government, or would like to browse for inspiration, try one of these Library of Congress call letters:
Locations of books
Many government documents are now published electronically. In Primo Search do a keyword search using terms that describe your topic, then use the left-hand facets to refine your search by Author/Creator: United States.
In addition, here are a few key sites for identifying and locating government documents:
Academic Video Online and Kanopy are streaming media services which provide access to a broad spectrum of educational and documentary content.