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:

• U.S. Congress. Congressional Budget Office: The CBO publishes numerous publications relating to national security, including:
• Congressional Publications: Access to hearings, committee prints, CRS reports, legislative histories, the Congressional Record, federal regulations, and the U.S. Congressional Serial Set. Many documents are in full text and cover the years 1789 to the present; others are citations that are available in full text in print or microform in the library.
• Congressional Research Service Reports: CRS, a branch of the Library of Congress, prepares research reports at the request of members of Congress, their staff, and Congressional committees.

• 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.

• US Trade Representatives Office Topics: USTR is an agency with decades of specialized experience in trade issues and regions of the world. It negotiates directly with foreign governments to create trade agreements, to resolve disputes, and to participate in global trade policy organizations.