I have studied this area extensively, since the WW2 Pacific Theatre has always been my favorite, and I never saw any compelling evidence that Roosevelt or anyone else in the U.S. high command "knew" Pearl harbour was coming.
Many people suspected in the fall of 1941 that Japan would not back down and would make a grab for the Dutch Indies but everyone thought the attack, if there was one, would be against the Philippines. No one thought the japanese had the capability to strike PH.
As to the interesting what ifs, there are a few:
1. what would the U.S. have done if Japanese forces had bypassed U.S. and British territory entirely and just invaded the Dutch East Indies? Could Roosevelt have convinced Congress to declare war to protect a european colony? after all, the US did not react when the Japanese took over french Indochina in sept. 1940.
2. what would the U.S. have done if on dec. 8, 1941, Hitler who had been kept in the dark about PH had disavowed his ally and declared war on Japan? Hitler was quite capable of turning on an ally if it suited him.
Roosevelt did not need PH to take the U.S. into WW2. Don't forget that in the fall of 1941, the U.S. was already fighting an undeclared war against Germany. U.S. Navy ships were escorting convoys in the North Atlantic and had depth charged U-Boats. The U.S. destroyer Reuben James was sunk by a U-Boat in october 1941. Many historians believe that Roosevelt was getting U.S. public opinion ready to declare war on Germany in the spring of 1942. PH just accelerated the process.
__________________
|