"On May 9, 2007, President George W. Bush issued National Security Presidential Directive (NSPD) 51, which is also identified as Homeland Security Presidential Directive (HSPD) 20, on National Continuity Policy. The directive updates longstanding continuity directives designed to assure that governing entities are able to recover from a wide range of potential operational interruptions. Executive branch efforts to assure essential operations are similar to those that are broadly integrated into many private sector industries. Government continuity planning also incorporates efforts to maintain and preserve constitutional government, based on the assumption that certain essential activities typically provided by government must be carried out with little or no interruption under all circumstances."
CRS Report for Congress, RS22674