If you have a limited amount of money and effort available for your presidential campaign, you don’t want to spend more in a state than you have to. The rules of the electoral college give all a state’s delegates to the candidate with the most votes. Once a candidate is confident that he will win 50.1% of the vote, therefore, it’s in his interest to begin to taper off his spending. He should start to divert his money to some other state, where he’s polling 49.9% or less.
Because of the fog of war, no candidate can knows for sure where he stands, and so no one would obey the 50.1%-rational-interest rule strictly. But as polling becomes more accurate and as ad purchasing becomes more sophisticated, one would expect the 50.1% rule to become more visible.
In other words, the hair’s-breadth finish of Florida 2000 might not be an anomaly. It might be a presage of the future. Barring reform of the electoral college, we should, perhaps, expect more and more swing states to be as close as polling and strategic advertising can make them.