FDR was, in fact, a victim of demonic possession.
His physical disability was the outward sign of the demon within. Little is known of the origin of this malignant spirit, except that it was almost certainly of celtic origin and took possession of the president in 1933. The 'New Deal' was not all it seemed. For those familiar with the old Scots language it was clearly a taunt: He was declaring himself the 'new de'il' - literally the new devil.
His hellish errand was to maximise the deathrate in the looming war, and all his efforts were plainly directed to this end. His first really overt action was to provide material support to sustain the UK war effort, thereby preventing the Germans forcing a peace deal. He also contrived to provoke Japan and thereby the US into war, he materially sustained the Soviets to prevent a quick German victory there and was working towards his master stroke of bringing the Western allies and Soviets into direct conflict in Eastern Europe when the strain on his host's body became too great and Roosevelt died.
Truman took office just in time to prevent the plot to reignite war between the West and the Soviet union, and he swiftly ended the war in the East by using the atomic bomb, which the possessed Roosevelt would never have done as it minimised casualties.
So, I'm thinking, Nicholas Cage, Michael Bay... Maybe a Baldwin as Truman. Not a good one, though.
Absolutely blowing at a cinema near you, really soon.