The Congress may determine the Time of chusing the Electors [of the President of the United States], and the Day on which they shall give their Votes; which Day shall be the same throughout the United States.
― Article 2, Section 1, Clause 4 of the Constitution of the United States of America.
Newsweek reports that the Department of Homeland Security is now looking into the possibility of finding legal justification for postponing the presidential election in case of an attack by terrorists.
The motor behind this request would seem to be "DeForest B. Soaries Jr., chairman of the newly created U.S. Election Assistance Commission. Soaries noted that, while a primary election in New York on September 11, 2001, was quickly suspended by that state's Board of Elections after the attacks that morning, 'the federal government has no agency that has the statutory authority to cancel and reschedule a federal election.' Soaries, a Bush appointee who two years ago was an unsuccessful GOP candidate for Congress, wants [Homeland Security Secretary Tom] Ridge to seek emergency legislation from Congress empowering his agency to make such a call." (quoted from the article)
Constitutionally, Soaries's comment is wrong. Congress, according to the Constitutional clause quoted above, does indeed have the power to reschedule a presidential election. I don't think that clause gives Congress the right to turn that power over to an agency of the executive branch. But then the Constitution also gives Congress the right ― and duty ― of declaring war, and for all intents and purposes Congress has already abdicated that power in favor of the executive branch; and I can't see a Republican Congress getting too het up about the possibility of ceding this power to the Republic President, especially if it looks like the election is going to be less close than they hope.
Incidentally, the argument quoted in the article ― "... the success of March's Madrid railway bombings in influencing the Spanish elections" ― is fallacious. It depends on reports of a poll showing that, before the bombings, Aznar would have won the election ― but we have never had any information about the date of the poll, the questions involved, or the part of the electorate polled. Actually, Spain seems to have become pretty anti-Aznar well before the election, largely due to his insistence on participation in the war in Iraq (which some 90% or more of the population opposed), his lackadaisicalness with regard to oil-covered beaches in northwestern Spain after a major maritime catastrophe, his treatment of peripheral ethnic groups such as the Catalonians and Basques, and his general behavior with regard to the proposed constitution of the European Union. But what really did him in at the end did have to do with the railway bombings ― the night before the election, someone in his government let it slip that Aznar & company knew all along that al-Qaeda was responsible, but insisted on continuing to blame the Basque ETA, in the hope of political advantage from this ― and the populace grew rightly annoyed about the fact that they had been lied to in such an important matter.
Well, truth to tell the record of the current administration suggests that after another terrorist attack on the United States, we might have exactly the same problem ...