“You do not seriously believe that a President would murder millions of civilians because of a successful attack on a purely military target, do you?”
Ask the relatives of the Japanese civilians who were “collateral damage” in World War II as a consequence of the attack on Pearl Harbor.
The decisions to incinerate Japanese cities were not made within days of the Pearl Harbor attack. They were made after 3 years of bloody, savage warfare and in the context of unsupportable (to Americans) losses on the battlefields in the Central and SW Pacific areas of operation. In the aftermath of Pearl Harbor, our war aims were to sweep the seas of the IJN and to thereby compel surrender to our long-term goals in East Asia.
I do not believe that Roosevelt would have ordered the incineration of Hiroshima and Nagasaki on December 8, 1941, and I bet you don't, either.