You're right about Americans mythologizing their WWII history: https://medium.com/exploring-history/wwii-mythologies-east-and-west-ab1b82774b1d . But the Russians, the Dutch, the Brits and the Italians do the same. I've written a WWII mythbusting tour series about all of them. The article link is about the Russian-American versions compared.

Your idea that the US might have entered WWII in 1939 is utterly fanciful. France and the Low Countries didn't fall until May-June 1940. Even as late as the autumn of 1941 85% of Americans surveyed wanted to stay out of the war, while the same % wanted to give all possible aid the UK and the USSR to fight the Nazis and aid the Chinese to fight the Japanese. The vast majority thought it possible to defeat fascism by supplying the Allies while staying out of combat. They turned out to be mostly right in Europe until the invasion of mainland Italy in September 1943. Until then most American casualties occurred in the air over Europe. Putting flying targets over Germany was the only second front aiding the USSR's fight against the Germans.

Most Americans, even racist Jim Crow southerners, didn't like Nazis. They were too unreflective to know how their country's segregationist laws and practices were a model for the Nazis to the point of Nazi lawyers visiting the American Bar Association to learn how to model the Nuremberg Laws on America's legally codified segregation system.