Americans at the time would not have supported intervention .. and the war machine knew it .. just as they know Americans would not be supporting our mindless 'war on terror' without 9/11.
The formula is simple.
The US was helping the European countries at war long before PH and in spite of the Neutrality Act and before the Lend Lease Bill was passed....
THAT was intervention....you don't have to send troops to intervene.....