There was an interesting Ask Historians thread about Nagasaki recently and the jist of it was that the decision to drop the second bomb wasn't made at the highest levels, or rather that it was hazily delegated much earlier and the call was made by local command. And because of local decisions, the moving up of the Nagasaki/Kokuro bombing by several days due to weather, makes it much harder to justify.
https://www.reddit.com/r/AskHistorians/comments/3c6xai/why_d...