Wiki - Truman's victory is considered to be one of the greatest election upsets in American history. Virtually every prediction indicated that he would be defeated by Dewey. The Democratic Party had a severe three-way ideological split, with both the far left (Henry A. Wallace of the Progressive Party) and far right of the Party (Dixiecrat Strom Thurmond) running third-party campaigns.
(Truman won 49.55% votes & 303 of the electoral college votes - A comfortable victory)
https://en.wikipedia.org/wiki/United_States_presidential_election,_1948https://www.usnews.com/opinion/articles/2008/10/30/past--present-harry-trumans-1948-comeback-campaignThe greatest comeback in politics took place 60 years ago, forever set into the political imagination by its capping image: Truman triumphantly holding a copy of the Chicago Daily Tribune with its banner headline. The Democratic Party consisted of "an unhappy alliance of Southern conservatives, Western progressive, and Big City labor."
Another big liability was an abject inability to deliver a prepared address: He had poor eyesight that prompted him to lean so far over his text that his audience would see the top of his head. He easily lost his place. He nasally droned through his texts so quickly that it seemed he was concentrating so hard on getting his words out that he could spare no thought for which to emphasize.
Truman btw explicitly campaigned on Single Payer which the AMA termed as "Socialized Medicine",
"Moscow line" & the GOP opposed. Truman castigated the AMA as "un-American" & later would say his failure to pass a Universal Public health insurance the most bitter & troubling disappointment of his presidency !
