Hasegawa makes a good case. The trouble is the obvious errors he makes, errors that anybody who actually knows the subject shouldn't be making.
For instance, page 18, he claims "Roosevelt immediately declared war". No, he didn't. Roosevelt couldn't declare war, though the declaration is commonly phrased that way: it wasn't a Presidential power; that power belonged to Congress. And it wasn't "immediate": it was the following day. (The same day Japan did, coincidentally; the notorious Fourteen-Part Message, commonly treated as a declaration of war, was, in fact, nothing of the kind.)
For instance, page 76, he calls "S-1" the Manhattan Project. It wasn't. S-1 referred to the atomic bomb, not the project at large.
For instance, page 126, he calls "the exchange of telegrams between Togo and Sato" "the Magic intercepts". They weren't. MAGIC referred to the decryption program and the intelligence derived from it--all of it. He further says "Naval intelligence was responsible for the Magic intercepts". Wrong again. The Army (what would become SIS) and Navy (ONI) both intercepted, and jointly decrypted, Japanese traffic. How does Hasegawa not know this?
For instance, page 140-1, he claims Fat Man "was detonated in Alamagordo". It wasn't in Alamagordo (or the town would be gone), but at the Trinity Site (the test stand). And it wasn't Fat Man, it was the same design: otherwise, Fat Man would never have been available for use. The second part is such an obvious mistake, it's stunning Hasegawa made it.
For instance, page 141, he misspells Admiral Leahy's name....
For instance, page 180, he says 70,000 buildings in Hiroshima were destroyed. He omits to say the majority had nothing to do with war production: the factories were mainly on the outskirts, and largely untouched.
For instance, page 181, he blithely repeats Truman's fabricated 1951 claim of a million casualties, and further says Truman was told this by his military advisors. This is false. The truth, as Truman well knew, based on contemporary documents, was more like 250,000 total U.S. casualties. This was not insignificant, but it amounted to a casualty rate approximately equal that of the invasion of Okinawa--& it went ahead to completion. How does Hasegawa not know this?
For instance, page 264, he states, "Had [Operation] Olympic [the invasion of Japan] been implemented, the result would have been an unprecedented bloodbath.", adding, "The Battle of Shimushu validates this assertion." This is utter nonsense. The Soviet capacity to land on a hostile shore was, if anything, less than Japan's, and Japan did not have a stellar record, contrary to the common public perception. The U.S., on the other hand, by this point had the finest amphibious landing forces and doctrine in history, and would have had control of the skies so complete, even the modern term "air dominance" pales somewhat. How does Hasegawa not know this?
These errors do call in question the caliber of Hasegawa's scholarship and serve to undermine my confidence in the quality of his case.
Page 76, FYI, he mentions Charles Cooke, omitting the commonly used nickname "Savvy", and fails to identify who the CNO was (Ernie King, if memory serves for date of office).