He wrote it as propaganda to convince the American public not to intervene against the Nazis.
Less than a year later, he was gung-ho for intervention because the Nazis had turned on Stalin.
No conscience, no shame.
I'm sure most Americans of that day fully registered the spookiness of Communist fanatics, who were out every day in front of the White House holding signs enjoining FDR against interference in European wars until the day Hitler invaded Russian-held territory (actually Polish territory), when they completely disappeared, overnight.
A day later they reappeared, holding different signs with warhawk messages, demanding that Roosevelt jump into the middle of Hitler's back.
As someone said in a different Hollywood venue, the Communists were certifiably "freakazoid".