“In 10 of the 15 presidential elections from 1944-2000, the candidate who was leading in the polls on Labor Day saw his margin shrink by the time of the final poll. (This includes Thomas Dewey, who managed to lose to Harry Truman in 1948 despite never trailing in the polls.) If you average together all 15 of those contests, the Labor Day spread was cut in half by Election Day—although the early leader won the popular vote in every case except Dewey-Truman. In other words, while last-minute poll tightening is far from death and taxes, it is a real phenomenon.”
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