U.S. Constitution
“The work of many minds, the Constitution stands as a model of cooperative statesmanship and the art of compromise.” The U.S. Constitution is referred to as “the law of the land” as it governs the way our society is structured, as well as outlining the general principles for which the United States will operate. State constitutions and local laws may be more restrictive than the U.S. Constitution, but may not be contradictory; i.e., they cannot permit at the state or local level something that is not permissible at the federal level.
http://www.archives.gov/exhibits/charters/constitution.html

Code of Federal Regulations
“The Code of Federal Regulations (CFR) annual edition is the codification of the general and permanent rules published in the Federal Register by the departments and agencies of the Federal Government. It is divided into 50 titles that represent broad areas subject to Federal regulation. The 50 subject matter titles contain one or more individual volumes, which are updated once each calendar year, on a staggered basis.” The Code of Federal Regulations is the “nuts and bolts” of our laws; unlike the broad strokes of the Constitution, the CFR is a more exhaustive detailing of how specific things are handled.
http://www.gpo.gov/fdsys/browse/collectionCfr.action?collectionCode=CFR

State Constitutions
States set laws beyond the U.S. Constitution; one of the founding principles of the United States is that each former colony would dictate its own laws. The federal government we know today has become much larger than its origin in the late 18th century, but the states still have the autonomy to pass specific laws as needed. As an example, here is a link to the Maryland State Constitution, adopted in its fourth (current) form in 1867:
http://msa.maryland.gov/msa/mdmanual/43const/html/const.html

PennState University Libraries Homeland Security Research Guide
Core documents relating to homeland security including the Bill of Rights, the U.S. Constitution, and all related acts, plans, directives, strategies, and the like.
http://www.libraries.psu.edu/psul/researchguides/socialsciences/homeland_security.html

Department of Homeland Security
Key DHS laws enacted after 9/11.
http://www.dhs.gov/key-dhs-laws

Naval Postgraduate School Center for Homeland Defense and Security – Homeland Security Digital Library
Federal policy and strategy documents
https://www.hsdl.org/?collection/stratpol&id=1935
Federal Executive Orders, issued by presidents of the United States while in office
https://www.hsdl.org/?collection/stratpol&id=eo
General U.S. policy documents
https://www.hsdl.org/?collection/stratpol&id=3
Presidential directives, organized by president
https://www.hsdl.org/?collection/stratpol&id=pd