National Security and Homeland Security Presidential Directive this is directive 51.
Summary: Presidential Directive 51: President Bush Can Cancel Elections ('Continuity of Operations') if there is an ECONOMIC crisis.
Do you think he will?
I think that the sad SOB who gets in will be left with a pretty fucked up country anyway but Bush has already deployed the army into USA in preparation for something to stop civil disobedience and possibly to enact corporal law.