One of Trumans successes was the use of atomic bombs to end the war with Japan. Harry Truman did not know of any atomic bombs before the death of Roosevelt. After he took office, he was shocked to learn about this development but decided to go ahead and use it. It proved to be good choice as less American lives were lost compared to if he had decided not to use the bombs.
His Truman Doctrine also prevented the spread of Communism. The Truman Doctrine stated that"It must be the policy of the U.S. to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures." He went on to help create Isreal.
Another one of Trumans successes was that his domestic changes. He raised the minimum wage, allocation of fedral funds for new housing, extension of social secuirty benefits, desegregation of the armed forces, and many more things. He also supported Civil rights legislation but met resistance in congress.
One of Trumans failures was also sort of a succsess. The atomic bombing killed 100,000 Japenese at the time of the explosion and 100,000 afterwards. He could have sought after a more peaceful way to end the war, instead he decided to just drop the bomb.