Truman's actions here must also be considered in light of the argument that he had been misled about the nature of the targets for the atomic bombings. From his diary in July 1945:

"This weapon is to be used against Japan between now and August 10th. I have told the Sec. of War, Mr. Stimson, to use it so that military objectives and soldiers and sailors are the target and not women and children. Even if the Japs are savages, ruthless, merciless and fanatic, we as the leader of the world for the common welfare cannot drop that terrible bomb on the old capital or the new."

"He and I are in accord. The target will be a purely military one and we will issue a warning statement asking the Japs to surrender and save lives. I’m sure they will not do that, but we will have given them the chance. It is certainly a good thing for the world that Hitler’s crowd or Stalin’s did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made the most useful..."

( http://www.dannen.com/decision/hst-jl25.html )

Truman also ordered the immediate cessation of further atomic bombings without his explicit approval on August 10th (the military was planning to continue the bombings as further cores became available, which were being produced at the rate of a couple per month).

See also http://blog.nuclearsecrecy.com/2014/08/08/kyoto-misconceptio...