OK, I’m willing to allow for conversation’s sake, as Dennis Miller did, that Truman was a war criminal.
Then to get back to the truth, Japan was a country that would not countenance any thought of defeat or surrender. At the time the bombs were dropped, Japan had already armed school kids with sharp bamboo sticks anticipating direct invasion of the Japanese homeland islands. We anticipated a million deaths on our own side in that invasion.
Although there are many things I don’t like about Truman, I think it’s entirely possible that he considered risking being tagged a ‘war criminal’ so he could spare the troops the horror of killing civilians and children in the invasion and being called 'war criminals’ themselves.
Apparently Truman meant it when he said that “the buck stops here”. That decision took courage and I admire it. Because he was willing to take that risk, a million or more sailors and soldiers were not exposed to blame or even criticism.
That is moral courage.