Well personally I wouldn't go off Electoral College numbers but more off of popular vote numbers, but to answer the question it's been varying over the last 100 years or so. 1916, 1948, 1960, 1968, 1976, 2000, 2004 were vary close elections. 1912 and 1992 were special cases because of the large third party presence and relegate those to what I would call the special elections catagory. From 1920-1940 you had the Era of Landslides, when economic factors, the Roaring Twenties and the Great Depression respectively, imbibed the specific parties with commanding support from the American people. 1944, 1988, and 1996 where what I'd put into the comfortable margin catagory with the rest, outside of the Era of Landslides, 1952, 1956, 1964, 1972, 1980, 1984, being true landslides.
For all those other years they all are shown to be in two catagories, either extremist opposition or great figure landslides. Extremist opposition is highlighted by the candidacies of both conservative Barry Goldwater and leftist George McGovern both of whose ideologies were far enough from the political centre at the time to ensure a large margin to the opponent. Great figure is highlighted in 1952, 1956, 1980, and 1984, when the two Republican behemoths of the last half century, Eisenhower and Reagan, were elected both for their personal charm, in Eisenhower's case his upstanding war record, and then guided their country through a time of overall prosperity, though both had to face economic downturns during their terms.
In 2000 and 2004, though, you did not have a great figure nor an extremist opposition, nor were their any great figures coatails, Clinton was a great president but he didn't create the same dynamism for future candidates that FDR or Reagan did, or opposition stupidity, to create a comfortable margin election. Both parties were headed by lacklustre figures who the general populace saw as respective of their parties positions on the issues. Thus without a charismatic charmer like Reagan or a person the populace viewed as an extremist like Goldwater or McGovern the election cycle became increasingly polarized between the opposing candidates and led to these close elections.
That is a very good explanation. I think we are now in an era of close elections - 2008 will definitely be close.
