On another note, I wonder whether FDR would have made the same choice as Truman in nuking Hiroshima.
We'll never know. But it's hard to imagine that Roosevelt wouldn't have made a similar decision when faced with the same facts that Truman was faced with.
Politically, it would have been impossible not to use it. The American public was in a rabid mood toward the Japanese, and if it was ever discovered, after we took a million casualties during a conventional invasion of Japan, that we had a superior weapon that could have forced an easier surrender but hadn't been used, the political consequences for the president who made that decision would have been catastrophic.