Columbia Libraries provide access to two different databases with declassified government documents. The Declassified Documents Reference System (access restricted to current Columbia affiliates) provides the full text of U.S. government documents which are routinely declassified, while the Digital National Security Archive (access restricted to current Columbia affiliates) includes documents which were declassified as a result of Freedom of Information Act (FOIA) requests.

Here’s an excellent guide to resources (both at Columbia Libraries and on the web) related to the U.S. Intelligence Community, maintained by one of my colleagues at Columbia.