Look at the date. This is Nov 44 when this attack occurs.
I am aware of that.
Do you think that the US will wait for the development of nuclear weapons, which the vast majority of the government don't even know of the existence of the Manhattan Project and with the exception of a few scientist who 'may be confident' that the a bomb will work?
Yes and no. Yes, they will wait on the atomic bomb before using poison gas, because that's just a horrible, horrible weapon (and I'm not talking in the horrible effects sense, because of course that's true).
No, they won't wait before they do any retaliation, but that will be more likely to take the form of advancing low-altitude firebombing (actually started in February 1945), aerial mining of Japanese seaways (actually began March 1945), and possibly delivery of biological agents (not actually carried out) than deployment of gas. Chemical weapons just aren't very useful strategically, despite what inter-war writers thought.