WWII was much easier to sell to the people, because the nazis were invading _now_. It seems impossible to sell reduced standard of living today to respond to a problem tomorrow
There was reluctance to act on an obvious and imminent threat. People just hoped it would go away.
If United States had joined the Axis powers, leadership very plausibly could have continued the practice of isolationism (which was the popular opinion before Pearl Harbor). It might have been a shortsighted move, but Nazis invading Europe did not sell the US population on entering the war.