This is an abbreviated version of a commentary originally published at The Hill

The “Dewey defeats Truman” upset election of 1948 is endlessly fascinating, an enthralling morality tale about the cockiness of pollsters, the credulity of journalists, and the hazards of glide-path campaigning.

Pollsters were confident that Thomas E. Dewey would unseat President Harry Truman — so confident that one of them, Elmo Roper, stopped releasing poll results in early September 1948, saying he was turning attention to “more valuable considerations.”

As is their wont, journalists took their lead from the polls, which showed Dewey comfortably ahead. In fact, some syndicated columnists wrote commentaries about what to expect from the Dewey administration ….