It's the most famous -- and infamous -- newspaper headline in American history: "Dewey Defeats Truman." On the eve of the 1948 presidential election, every major political poll predicted a landslide victory for Thomas Dewey, the Republican governor of New York, against the unpopular incumbent, Harry Truman. Truman's Democratic party had been crushed in the 1946 midterm elections, saddling the new president -- Dewey assumed the office in 1945 after the sudden death of Franklin D. Roosevelt -- with an opposition-led "do nothing" Congress [source: Miller Center]. The Democrats also suffered a blow during the Democratic primaries, when Strom Thurmond and the "Dixiecrats" jumped ship to form their own party.
All of the momentum was in the Republican's camp, and Dewey knew it. The candidate had run in 1944 and narrowly lost to a much more formidable foe in FDR. (Some blame his mind-bending campaign slogan: "Dewey or Don't We." Nope, no question mark.) With the political winds in his favor, Dewey chose to take a prudent tack. While Truman crisscrossed the country on "whistle-stop" train tours, preaching New Deal policies and bold civil rights reforms, Dewey stuck to bland, non-boat-rocking generalities [source: Miller Center]. As a result, Dewey developed a reputation as the dullest man in the room, but the polls still had him leading by a wide margin with only weeks left until election day.
Looking back on their mistake, the good folks at Gallup found several flaws in their polling methods. For starters, they stopped polling three weeks before the election. And more importantly, they polled a representative (not random) sample of Americans of voting age, but not necessarily Americans who were most likely to vote. Truman's tireless campaign efforts brought out a strong union vote, while the overconfident Republican base "played golf that day" [source: Jones].
Predicted to lose by five to 15 points, Truman won by 4.4 percent of the vote. On a train ride back to Washington D.C. two days later, a staffer found an early edition of the Chicago Daily Tribune under a seat. In the famous picture of the infamously wrong headline, Truman's impish grin says it all: Dewey blew it.