“We tried isolationism in 1940. War came to us anyway, and it was all the worse for our having delayed.”
Not quite. Roosevelt had an active policy to oppose the Axis and aid the Allies. Remember “Shoot on sight”, “rattlesnakes of the sea”, and escorting convoys in the western Atlantic. One of the reasons Hitler declared war on us. Then Lend-Lease and embargos against Japan.
Once Britain declared war on Japan, that removed any constraints we had to aid Britain.
Only would have been a matter of days before a U-Boat sunk a US ship and we declared war on Germany, even if Hitler didn’t declare war on us.