From the Summary: "As part of his response to the September 11, 2001, terrorist attacks against the World Trade Center in New York City and the Pentagon in Washington, D.C., President George W. Bush formally declared national emergencies on September 14 and 23. The President's actions follow a long-standing tradition of alerting the nation to a crisis threatening public order and constitutional government. Under current arrangements, such declarations also allow the President to make use of activated authority on a selective basis, as appropriate for responding to the emergency at hand. Some 60 provisions of law may be brought into force by an emergency declaration. Updated as events recommend, this report chronicles the actions taken by President Bush pursuant to his national emergency declarations, as well the issuance of additional such declarations concerning terrorism."
Library of Congress. Congressional Research Service