He did not have options presented to him. This is a crucial thing to keep in mind: the narrative about him weighing all sorts of options and making a tough decision is totally misleading. It was assumed the United States would use the weapon — everything done with regards to it had this in mind. The only "choice" that Truman himself was personally presented with was whether to bomb Kyoto or not — a question of targeting (he agreed with Stimson, who presented the option, that a "military" target like Hiroshima was a better target than a "civilian" target like Kyoto). He was also able to set the specific timing of the first use (no earlier than August 3rd, so that the Potsdam Conference would be over, but before the Soviets declared war against Japan). As far as we know Truman was never presented with the possibility of "demonstrating" the weapon on an uninhabited area, and nobody thought (including himself) that the Japanese should be warned (the whole point was to surprise them). These questions were discussed at lower levels (e.g. the Interim Committee), but those discussions didn't go to Truman himself.