Here's the report for August 3, 1945. As the first bomb is readied on Tinian, Truman learns of new Japan surrender overtures.
One of his top aides in on that conversation, chairman of the Joint Chiefs, Admiral William Leahy, would later denounce the decision to use the bomb: "[T]he use of this barbarous weapon at Hiroshima and Nagasaki was of no material assistance in our war against Japan. The Japanese were already defeated and ready to surrender.... [I]n being the first to use it, we...adopted an ethical standard common to the barbarians of the Dark Ages. I was not taught to make war in that fashion, and wars cannot be won by destroying women and children."