Such an emergency is defined as "any incident, regardless of location, that results in extraordinary levels of mass casualties, damage, or disruption severely affecting the U.S. population, infrastructure, environment, economy, or government functions.

"[1] The unclassified portion of the directive (which replaced President Bill Clinton's 1998 Presidential Decision Directive 67), was posted on the White House website on May 9, 2007, without any further announcement or press briefings,[2] although Special Assistant to George W. Bush Gordon Johndroe answered several questions on the matter when asked about it by members of the press in early June 2007.

The source text indicates that during a catastrophic emergency the federal government will cooperate as a matter of comity in order to protect the constitution: (e) "Enduring Constitutional Government," or "ECG," means a cooperative effort among the executive, legislative, and judicial branches of the Federal Government, coordinated by the President, as a matter of comity with respect to the legislative and judicial branches and with proper respect for the constitutional separation of powers among the branches, to preserve the constitutional framework under which the Nation is governed and the capability of all three branches of government to execute constitutional responsibilities and provide for orderly succession, appropriate transition of leadership, and interoperability and support of the National Essential Functions during a catastrophic emergency;[3]The source text for NSPD51 repeatedly reaffirms constitutionality and specifically states that "(9) Recognizing that each branch of the Federal Government is responsible for its own continuity programs, an official designated by the Chief of Staff to the President shall ensure that the executive branch's Continuity of Operations and Continuity of Government policies in support of Enduring Constitutional Government efforts are appropriately coordinated with those of the legislative and judicial branches in order to ensure interoperability and allocate national assets efficiently to maintain a functioning Federal Government."

The directive further says that, in the case of such an emergency, the new position of "National Continuity Coordinator" would be filled by the assistant to the president for Homeland Security and Counterterrorism.

While similar executive security directives have been issued by previous presidents, with their texts kept secret, this is the first to be made public in part.