Let’s say that Germany accidentally sinks an American ship in September 1939. Americans are angry but not really looking for war. FDR claims that in order to ensure we don’t have to fight, we need to send aid to Britain/France so they can win. FDR gets some sort of Lend Lease bill through Congress by the end of September before the public calms down.
Would Lend Lease starting in September of 1939 make a difference? And if not, would Lend Lease following Germany’s betrayal of the Munich Agreement make a difference? Or Lend Lease starting during the Munich Agreement?
Also, if it was later expanded to Finland and China at the start of the Winter War, would it change anything there?
I don’t consider these scenarios very likely, but am curious.