The question dealt with cancellation of elections but one member feels the need to inject racist remarks into the discussion. So, whenever you brush off charges of racism, remember the comment below, totally uncalled for and off the subject.
"Your talking Obama the Magic Negr0, he can make anything happen just ask him"
Good question. Authority is delegated to Congress and not the president:
Because of the fear of possible terrorist attacks which could be directed at
election facilities or voters in the States just prior to or during the elections in a
presidential election year, attention has been directed at the possibility/authority to
postpone, cancel or reschedule an election for federal office. The United States
Constitution does not provide in express language any current authority for a federal
official or institution to “postpone” an election for federal office. While the
Constitution does expressly devolve upon the States the primary authority to
administer within their respective jurisdictions elections for federal office, there
remains within the Constitution a residual and superceding authority in the Congress
over most aspects of congressional elections (Article I, Section 5, clause 1), and an
express authority in Congress over at least the timing of the selections of presidential
electors in the States (Article II, Section 1, clause 4). Under this authority Congress
has legislated a uniform date for presidential electors to be chosen in the States, and
a uniform date for congressional elections across the country, which are to be on the
Tuesday immediately following the first Monday in November in the particular,
applicable even-numbered election years.