I’ve had discussions over the years with people about this. Some say that we should not have dropped the bombs, because Japan was already so weak and on the verge of surrender.
Some say we should have dropped a bomb offshore in the Pacific somewhere, to show the Japanese the power of the bomb we had, and tell them if they don’t surrender, we will use these bombs for real on them. I don’t know how well that would have worked, because we only had a handful of bombs ready to go at that point in time. And then we would have had one less to use for real, if we did the demonstration, but the Japanese called our bluff.
The japanese didn’t believe us after the first bomb.
Truman didn't even know about atomic bombs and that we had created them until a few weeks AFTER he was sworn in as president.
Stalin knew about the Manhattan Project a year or more before Truman did.
Truman pulled Stalin aside at Potsdam, just the two of them and Stalin's translator. That's when Truman first "told" Stalin about the weapons. Of course, Stalin knew all about the project and that Russia had successfully infiltrated it. He probably knew more about the U.S. effort than Truman did.
From the text the mention of “James Bryant Conant, president of Harvard and chairman of the National Defense Research Committee ...” is noteworthy,
Conant was an exceptional person. He was a brilliant chemist who became the first president of Harvard not from the “community”. It’s not generally known that he headed the bomb project.
With only two bombs of different design and the material for possibly a third, the performance of the first two wasn’t 100% certain. That means a demonstration was out of the question.
Conant’s granddaughter wrote an excellent biography of the man if you’re interested.