Here's a very simple question:
Suppose that on November 24th, the USA, after breaking Japanese Codes (I believe that had done so before Pearl Harbor) learns that Pearl Harbor is going be hit on December 7th?
Granted that FDR wants a war, but this puts him in a very awkward situation. On one hand, if knows of the attack and it confident that it will happen (as I suggest), failing to respond to it before it happened could well result in his impeachment. On the other hand, going public with the knowledge would almost certainly scare off the IJN and the USA would be unenthusiastic about the war without Pearl Harbor.
What would likely happen?