Years ago, when I lived in San Diego, I saw a Cadillac with a homemade sign taped to the window that read "If there was not a Pearl Harbor, there would not have been a Hiroshima." The car's specialized license plate indicated that the owner was a Pearl Harbor veteran and recipient of the Purple Heart. The combination of messages perfectly encapsulated what is often the American understanding of the atomic bombs: necessary, just and, above all, uncomplicated.

Tomorrow, Barack Obama will become the first sitting U.S. president to visit Hiroshima. It is a powerful moment for both Americans and Japanese. As a historian, I hope we can see this visit as an opportunity to open up the debate on the standard narratives of the nuclear attacks.

No American president has ever entertained visiting Hiroshima or Nagasaki. Certainly, no U.S. president or politician was ever going to apologize for the use of atomic bombs. Doing so, the rationale goes, would raise demands for reparations from victims and vilify U.S. veterans.