President Bush, without so much as issuing a press statement, signed a directive that granted near dictatorial powers to the office of the president in the event of a national emergency declared by the president. Basically Martial Law.
The "National Security and Homeland Security Presidential Directive" NSPD-51, loosely defines "catastrophic emergency" 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."
When the President determines a catastrophic emergency has occurred, the President can take over all government functions and direct all private sector activities to ensure we will emerge from the emergency with an "enduring constitutional government."
Translated into layman's terms, when the President determines a national emergency has occurred, the President can declare to the office of the presidency powers usually assumed by dictators to direct any and all government and business activities until the emergency is declared over. Including cancelling the Presidential Election.