FDR was trying a very straight forward copy of the game that brought America into WWI - provoke the Germans into provoking America into getting into a war with them. However, until December 1941 Germany did not want to play.
I agree on this point.
Alternate history is fun topic, especially with a few beers and rationale debaters.
But, in the end, the certainty of the failure of Fascism in WW2 is clear.
First and foremost is logistics. In population, production, and resources (especially oil,) the Axis were deficient. Amateurs talk of tactics. Professionals talk of logistics.
Second, people get hung up on the illusion of invincibility. Early victories were over weaker adversaries: Denmark, Norway, Belgium, Luxembourg, The Netherlands, France, Yugoslavia and Greece. France was not weaker on paper, but was not prepared or motivated to hold out. These early successes are as much about being ready and willing versus being able.
After other combatants mobilized, and figured out the blitzkrieg, it was a war of attrition the Fascists could not win, regardless of hair color and eye color.
Finally, the US was going to get into the war eventually. Conscription was signed into law in September 1940, after the fall of France. The USN escorting convoys as far as Iceland by April 1941. The fleet move to Pearl Harbor and movement of aircraft to the Pacific was a sign of things to come.
It is not just Germany and Japan. History is littered with those who doubted the American capacity for belligerence. From the outside, the US has often seen as a bunch of decadent hedonists. More foreign tourists need to come to Texas.
Some statistics, courtesy of
www.world-war-2.info/statistics/Oil production in tons:
Germany
1939 8 million
1942 7.7 million
1943 8.9 million
1944 6.4 million
US
1942 184 million
1943 200 million
1944 223 million
Total for WW2
Aircraft World 542,000
Aircraft US 283,000
52% US
Total for WW2
Vehicles World 5.1 million
Vehicles US 2.47 million
48% US