First off, presume that Attack on Pearl Harbor never took place, this does not mean the US would not have have entered WWII.

One reason why there has been a persistance charge that FDR et al had been conspiring on the morning of 7 Dec. was because there is evidence that that there was a conspiracy to get the US into the war through the back door of a causis belli with Japan -- just that this conspiracy did not involve Pearl harbor in and fashion. No, that attack came as a complete surprize.

The FDR conspiracy involved in creating an artificial causis belli but having the IJN obliging the US by sinking an "American Flagged" vessel. It was though the main IJN fleet was steaming south toward Indochina, so the plan was to lease three (3) fishing trawlers in the vicinity of Manila Bay, put a US Officer (ensign) and an US flag (another type of ensign) on these ships, then sail them such to encounter the IJN fleet and draw fire.

Alas, the IJN fleet was not steaming south past the port of Manila. As it turned out one sent sail leaving the harbor, another was just getting underway, and the last never got organized when the "Air Raid -- Pearl Harbor. This is no drill." message was recieved, scuttling the plan.