It was certainly talked about at the time. On the night of the attack, at least one senator made the comment that Roosevelt had deliberately allowed the Japanese to attack as a “back door” to get us into war. Colonel Charles Lindbergh Jr. even agreed with a friend who stated the same.

There were two notable figures who were determined conspiracy theory advocates. Harry Barnes and John Flynn were both very vocal opponents to entering the war and both felt FDR would do anything, including murder, to drag the nation into it. Barnes had even written some books about it, but the publisher made him rewrite sections to make them more patriotic. Flynn also wrote a book; however he never believed FDR knew when and where the attack would occur, just that FDR purposely provoked it.

Roosevelt made a pretty easy target of himself for these types of allegations. His Asian foreign policy was intensely secretive, and he had made some choices in regards to events in Europe which almost forced Japan to act. After the attack he is known to have tried to hide documents in an effort to have the commanders at Pearl take the full brunt of the blame.

FDR had already signed off on a limited embargo of high-octane aviation fuel and good quality metals to Japan in July, by September he was ready to ban all metal exports to the nation. Japan saw the oil embargo as an act of war. Adding further fuel to the fire FDR also announced a $100 million loan to China; three days later Japan signed the Tripartite Pact with Germany and Italy.

The United States had developed a way to break the Japanese cryptography used to communicate with its ambassadors under the code name of Magic. Because we had been reading their messages Army cryptographers knew Japan had been gearing up for war, but did not know exactly when or where. Magic was a very closely guarded secret and knowledge of it was limited. After messages had been decoded they were placed into locked briefcases and delivered only to top military and civilian officials; the commanders at Pearl didn't get copies.

One of the greatest fallacies of the attack on Pearl Harbor is the alleged intercepted message from Japan to its ambassadors stating they were going to attack the naval station; this is untrue. The Japanese ambassadors to the US never knew where or when the attack was going to happen, only that at some point one would occur. The US was actually expecting an attack in the Philippines. After the attack occurred most Americans didn't really consider a true conspiracy because they had other things to worry about.

Pearl Harbor: FDR Leads The Nation Into War

Real Enemies: Conspiracy Theories And American Democracy, World War I To 9/11