Many Americans had been suffering loss, whether that be property, money, and jobs from the great depression, or loved ones from ww1, America as a whole was grieving. American isolationists did NOT want to have themselves be involved in European/Asian conflicts, as well as other international policies.
So to answer the main question, Americans are most likely to have isolationist feelings when the country itself is suffering a loss.
Hope this helps!
-Moiselle
