For more see the Government Information portal at Columbia. If you are unfamiliar with how the American Government is set up (it's confusing!) please consult this fabulous set of resources from U.S.A.Gov.
Some useful places to begin:
Government Accountability Office (GAO) : Known as "the investigative arm of Congress" and "the congressional watchdog." GAO supports the Congress in meeting its constitutional responsibilities and helps improve the performance and accountability of the federal government for the benefit of the American people.