"So, now, after the successful test, if you use one of the two bombs as a "demonstration", you've only got one left. If they don't surrender after the "demonstration", you can deliver one bomb...and that's it.
Wouldn't that be cutting things a little close?"
It would not be cutting it close for the hundreds of thousands that died at Hiroshima and Nagasaki.
Don't get me wrong - its hard to argue with success and the bombs did succeed in a early end to the war.
But what if the bomb was dropped in a forested area that would readily demonstrate the power - and if it did not work, none would be the wiser.
Just thinking out loud. Also, were we not to wipe out so many civilians, it might not have rattled the Russian cage - which only got us into a very expensive arms race.
And that is the answer, isn't it? What was done achieved the desired result. It WORKED!
Even though it may have come at the cost of the lives of several hundred thousands at Hiroshima and Nagasaki, the apparent alternative was several hundred thousands of allied lives (mostly American) and several millions of Japanese.
Any solution that tried to get cute with those odds ran the risk of being "too clever by half".