In the 1940s the Chicago Tribune was a notoriously Republican newspaper that had no love for President Harry Truman. In an editorial leading up to the election of 1948, the Tribune had referred to Truman as a "nincompoop". As the November 2nd Election Day approached, the outcome appeared clear and never in doubt. The polls and the pundits all agreed that New York Governor Thomas Dewey, the Republican candidate, was going to win the election and become president. But the Tribune wanted to stick the fork in Truman and be the first newspaper to report it. In fairness, everyone agreed on what the outcome would be. Everyone, except for Truman that is.

Polling has never been an exact science, and it was less so in 1948. But Truman had low favorability numbers in the polls, and he was the leader of a divided party. Southerners disliked the passage of a civil rights platform at the Democratic convention. Southern Democrats split from the party and supported Governor Strom Thurmond of South Carolina for president. Liberals on the left wing of the party also bolted for their own candidate, former Vice-President Henry Wallace, who ran as the candidate of the Progressive Party. With his party divided, Truman faced off against Dewey, the leader of a united Republican Party.
Undeterred, Truman toured the country, often speaking from the back of his campaign train, to large, enthusiastic crowds. "Give 'em hell, Harry" became a popular slogan shouted out at stops along the tour. Truman would respond, "I just tell the truth and it feels like hell to the Republicans." But despite Truman's optimism and resolve to never give up, the polls and the pundits all believed that Dewey's lead was insurmountable, and that Truman's efforts were for naught. Truman's own staff didn't even think he could win, and his wife Bess had doubts as well about whether her husband could win. The only person who appears to have considered Truman's campaign to be winnable was Truman himself, who confidently predicted victory to anyone who would listen to him.
As the campaign drew to a close, the polls showed Truman was gaining. Dewey's Gallup lead dropped from 17 points in late September to 9 points in mid-October to just 5 points by the end of the month, just above the poll's margin of error. Although Truman was gaining momentum, the conventional wisdom was that it was too little, too late. On September 9, pollster Elmo Roper proclaimed, "Thomas E. Dewey is almost as good as elected. I can think of nothing duller or more intellectually barren than acting like a sports announcer who feels he must pretend he is witnessing a neck-and-neck race." Roper stopped polling voters until the final week before the election, when he took another poll. He said that it showed a slight shift to Truman, but claimed that it still gave Dewey a huge lead.
In the campaign's final days, many newspapers, magazines, and political pundits were so confident of Dewey's impending victory they wrote articles to be printed the morning after the election speculating about the new "Dewey Presidency." Life magazine printed a large photo on the cover of its final edition before the election, with the caption: "Our Next President Rides by Ferryboat over San Francisco Bay".
Newsweek polled fifty supposed political experts and all fifty predicted a Dewey win. Several well-known and influential newspaper columnists, such as Drew Pearson and Joseph Alsop, wrote columns to be printed the morning after the election speculating about Dewey's possible choices for his cabinet. The day before the election, Pearson wrote that Truman's election was "impossible". Walter Winchell reported that gambling odds were 15 to 1 against Truman. More than 500 newspapers, accounting for over 78% of the nation's total circulation, endorsed Dewey. Alistair Cooke, the distinguished writer for the Manchester Guardian newspaper, published an article on the day of the election entitled "Harry S. Truman: A Study of a Failure." For its television coverage, NBC News constructed a large cardboard model of the White House containing two elephants that would pop out when NBC announced Dewey's victory. The did not plan for the contingency of a Truman victory.
As Truman made his way to his hometown of Independence, Missouri, to await the election returns, some among his inner circle had already accepted other jobs, and not a single reporter traveling on his campaign train thought that he would win.
On election night, a press deadline required the first post-election issue of the Tribune to go to press before even the East Coast states had reported many results from the polling places. The paper relied on its veteran Washington correspondent and political analyst Arthur Sears Henning, who had predicted the winner in four out of five presidential contests in the past 20 years. The editors of the Tribune decided that the first edition of the paper would go to press with the banner headline "DEWEY DEFEATS TRUMAN".
The story by Tribune correspondent Henning also reported Republican control of the House of Representatives and Senate that would work with President-elect Dewey. Henning wrote: "Dewey and Warren won a sweeping victory in the presidential election yesterday. The early returns showed the Republican ticket leading Truman and Barkley pretty consistently in the western and southern states."
As returns began to indicate a close race later in the evening, Henning stuck by his prediction. Thousands of papers continued to roll off the presses with the famous headline. The paper's lead story was rewritten for later editions to emphasize local races and to indicate the narrowness of Dewey's lead in the national race, but the same headline was left on the front page. Only late in the evening did the Tribune change the headline to "DEMOCRATS MAKE SWEEP OF STATE OFFICES" for the later two-star edition. Some 150,000 copies of the paper had already been printed with the erroneous headline.
As we know now, Truman won the electoral vote by a 303–189–39 majority over Dewey and Thurmond. Instead of a Republican sweep of the White House and retention of both houses of Congress, the Democrats not only won the Presidency, but also took control of the Senate and the House of Representatives.

When Truman was passing through St. Louis on the way to Washington two days later, he stepped to the rear platform of his train and was handed a copy of the Tribune early edition. Happy to exult in the paper's error, he held it up for the photographers gathered at the station, and the famous picture was taken.
Many years later, Tribune publishers were able to laugh about the blunder. They planned to give Truman a plaque with a replica of the erroneous banner headline on the 25th anniversary of the 1948 election, but Truman died on December 26, 1972, before the gift could be bestowed.