Harry Truman was the 33rd President of the United States and the one who authorized the lunching of the atomic bomb on Japan in 1945. He said that a president has to make toughs decisions, and if you were not able to do it, you have no business being the President.
He was always fighting with Congress and the Senate because he wanted to bypass then on key decisions like going to war. He just did that by entering the Korean war without formally participating the Senate, calling it a "police action" rather than a war.
During his presidency, he established The National Security Council and the Central Intelligence Agency. The main purpose of these organizations was to provide direct advise and all source of information directly to the President, without informing The State Department or Congress.
By doing all these actions, President Truman exercised an increase of presidential powers and that was his goal from the start. He wanted the Chief Executive position to have more freedom and to act independently without congressional supervision.