You are doing great work, thank you again.
I think FDR was more farsighted than most isolationist Americans of his time. But doubt if in April 1939 he considered a war requiring US intervention as inevitable. No doubt, he believed some effort to avoid war was necessary.
But your comment about "moral high ground" makes a good point: for the western democracies in the 1930s, there could be no such thing as "preemptive war," or a "military police action," or a "war to liberate countries from fascism." There were no UN resolutions and the US had no NATO "one for all and all for one," type treaties. There was no way that FDR could "draw a line in the sand" and threaten a US military response if Hitler misbehaved.
And remember, many if not most Americans believed German false propaganda claiming Germany was innocent of starting the First World War. It was therefore completely necessary for Americans to be 100% convinced that the NEXT war was 100% caused by German aggression.
"Moral high ground" is exactly right. Americans in 1939 (as today) would fight and die for nothing less. FDR knew that full well. So: ONLY a direct attack could bring the US into a "foreign war."
And that meant FDR could only wave an olive branch at the fascist monsters, in hopes its sweet smell might somehow calm their animal spirits.
Of course, it didn't work.