“President Truman said the almost the exact same thing about Japan just before the atomic bomb was dropped.”
Actually he said it after Hiroshima was laid waste, but before the second was unleashed upon Nagasaki.
Japan never would have surrendered if they had known that we had used up our entire inventory of atomic bombs. It was only by convincing Japan that we would keep nuking them until the Japan was a sheet of glass that they agreed to surrender.