Harry Truman's victory in the 1948 presidential election is one of the most legendary moment in American politics. His party was divided and did not want him to run. Nearly every political scientist at the time said Thomas Dewey would win. However Truman would not quit. He choose to campaign all across the country, railing against his "Do-nothing" congress, and eventually winning the Presidency. I already know that story. What I want to know is why did Dewey lose? Again, so people many thought he would win. Where in his campaign did he go wrong? Why did the man whom so many political scientists thought would win end up losing the presidential election?
Both parties were split down the middle during the 1948 election. The Dixiecrats were the far more racist and more conservative branch of the Democratic party, however the lesser known split was in the Republican party.
Dewey, even for a Republican at the time, was still quite liberal, and his platform included civil rights legislation, expansion of social security, promotion of health and education by the government. However, the majority of the Republicans were far more conservative than Dewey, and it should be noted that the Republicans controlled both houses of Congress with a majority.
Truman called for a special session of Congress, at 1:45 AM, 4 months before the election, with an approval rating of 36%. This is famously now called the Turnip Day Session, which lasted 2 weeks. Truman basically called the Republicans bluff on their liberal policies that were drafted during the Republican convention under the leadership of Dewey, challenging them to live up to their promises of civil rights legislation, health care and education reform, etc. Both houses refused to sign any bill during the two week session.
Truman called this the "Do nothing eightieth congress" as proof of the lack of competence in the Republican party and revealed to the public that the Republicans could not deliver what they were promising.
Dewey did nothing wrong, in fact, he was doing everything he could, he was trying to liberalize the Republican party for the more liberal American populace, he was popular as can be, and the Republicans were at a high point, controlling both houses, Truman's popularity in the polls, a general popularity of the Democratic party decreasing, a split in the Democratic party and potentially losing the "solid south." However, Truman saw the split in the Republican party as well and was able to exploit it, knowing that the more experienced and more conservative members of congress would never approve of anything the new Republican administration was trying to push, and this obviously resonated with people more than anyone could ever think.
There have been other small things that have been attributed to Truman's successful campaign, such as the campaign film for Dewey was a very high budget film portrayed him as more distant from the average person whole Truman's campaign film was obviously very low budget and portrayed him more as more engaged with the average person.
In short, Dewey did nothing wrong, but Truman did everything right.