In a recent Radiolab episode, Nukes (at the 15 minute mark), historian Alex Wellerstein argues that the evidence available suggests Truman was not aware that cities were being targeted by nuclear bombs, and was under the impression that the targets would be purely military.
Wellerstein's blog post goes into detail on this, identifying a key discussion during the Potsdam Conference between Truman and Stimson, where a misunderstanding appears to have led Truman to be spectacularly misinformed. How accurate is this? It seems like the evidence is compelling but not necessarily conclusive, is there any contradictory evidence?
Alex Wellerstein is also known as u/restricteddata, and has answered a ton of questions for us here. You may be interested in this section of our faq: https://www.reddit.com/r/AskHistorians/wiki/faq/militaryhistory/wwii/usa#wiki_the_atomic_bombs.2C_aka_questions_.2Fu.2Frestricteddata_has_answered
It seems like the evidence is compelling but not necessarily conclusive, is there any contradictory evidence?
It is an interpretive argument, to be sure. There are gaps in our ability to reconstruct exactly what Truman thought. In my longer work on the subject (still being finished), I talk about exactly when and where I am making interpretive leaps (and chide historians on this subject who make said leaps without indicating they are doing so).
As for "contradictory evidence," there are only really two issues I have come across, other than people saying, "oh, well SURELY the President knew" which I don't consider to be evidence-based. They are:
Truman's own after-the-fact accounts always puts him in charge and in the know on everything. I think these are false and a story he started to tell himself (and others) post-Nagasaki, esp. when the atomic bombings started getting criticized in 1946-1947 (which is where a lot of the "decision to use the bomb" narrative comes from). The fact that Truman's memoirs, etc., are at odds with the historical record on many issues is easy to establish and has been established as a fact by historians for a long time now, so I don't consider this a serious challenge.
The more tricky thing is that there is one timeline issue that I find hard to resolve, and it depends on exactly when Truman wrote a specific letter and exactly when he heard about the casualties of Hiroshima. Specifically the letter to Russell on the 9th. Did he write that before or after he realized it was a city? It's hard to pin down. Russell wrote to Truman on August 7th, definitely before Truman heard any casualty estimates. Truman could have theoretically heard about them on August 8th. We know that by August 10th Truman definitely understands it, and may have understood it by some point on August 9th. If Truman knew Hiroshima was a city before writing to Russell that complicates the argument a bit (it doesn't invalidate it, but it changes the Russell letter from being a misconception and into something slightly different — e.g., an expression of remorse on some level). But anyway, this gives you a slight taste at the difficulties here, trying to track down exactly when Truman knew something, exactly when he wrote something, etc. (And not just Truman — his speechwriters, etc.) A lot of the "work" of my research into this topic has been trying to very precisely pin down a lot of "what did Truman know and when" sorts of questions, many of which, as far as I can tell, have not been pinned down as well by historians in the past, because without an argument like this to motivate you, you don't really have to (it doesn't matter as much if you think Truman essentially knew what was going on). Which is just to say, I recognize there is a high evidentiary burden for such an argument, and I do think it can be made plausibly.
Now, again, this is an interpretive argument based on the evidence base we have (the archival documents) and also is about rejecting a certain evidence base (the Truman memoirs, etc.) on methodological grounds. All historical work is of similar character, but I don't want to overstate or understate things. I find it to be a very compelling interpretation, one that makes a lot of things in the final days of the war make more sense (as well as Truman's post-war feelings towards the bomb, which are not enthusiastic to say the least — he jealously keeps them from the military, not trusting them again with such matters, something that makes, in my eyes, much more sense if he was feeling "burned" by them).
But scholars can and do disagree on such things. The most recurrent objection I have gotten when I present this at conferences, etc., is mostly an emotional one: "I just can't believe that the President would be so uninformed," but the bulk of my work on the subject is trying to conjure up the context in which that would happen (and, again, I think it's pretty compelling).