The questionable value of precedent in politics

From the web comic xkcd, by Randall Munroe

Before 1936, Maine was perceived by the chattering class as the ultimate bellwether state: "As Maine goes, so goes the nation."

After 1936, the saying had to be amended: "As Maine goes, so goes Vermont." Although Maine had voted Republican in 1936, Alf Landon did not defeat FDR. Landon carried only Maine and Vermont in the general election.

Mr. Munroe's many other examples here are worth considering as one considers the grave (and contradictory) prognostications of political columnists and TV talking heads.