The 1948 Truman-Dewey race is one of the great upsets of all time in the USA. Truman was Vice President in the last term of FDR, and took over only a few months after FDR took office after the start of his 4th term as US President. Truman was a senator from Missouri prior to being chosen as VP
in the 1944 election. He was chosen as he went after war profiteeirs and people whom didn't meet military contract standards as a Senator. He was the President who - for better or worse - made the decision to drop the atomic bombs in Japan. As acting Presidnet, he made the first steps in racial desegeration in the USA, by desegerating by race the US Military and was the force behind the USA to be the 1st major nation to recognize Isreal. In the run up to the election of 1948, Truman was way behind - 12-15% points behind Dewey, who was a state Proscuter in Manhattan, NYC and then Governor of NY State. Truman then went on a long train campaign tour, he bertated the 'do nothing' Republican dominated Congress, and won by a significant margin.
The 1960 JF
Kennedy (D) vs. Nixon (R) race was one of the closest until the 2000 election. Supposdly, the 'dead' voted from their graves in the Chicago area of ILL for Kennedy, and thus won with other states, enough to badly beat Nixon in terms of electorial votes. The popular vote margin for Kennedy was estimated at about 200,000, or about 1 vote for each voting district in the USA at the time.