I had heard talk that FDR knew of the planned attack but let it happen to leverage the event to motivate the American people to pull the country out of the depression, which basically lasted until the war effort. Prior to that, his commie policies dissuaded people from being very productive because - well, why buy the cow when the government will steal it and give the milk away.
Except they thought the attack would be in the Philippines! Pearl Harbor was far to bold to consider.
Sadly my father thought FDR was the greatest and my father as not a dumb man just a union Democrat born in 1910.