At the time, the Lend-Lease Act was a largely popular move away from non-interventionism. Anti-German propaganda (the word isn't always a bad one) and news reports from continental Europe had swayed public opinion toward aiding Britain.

But there were still those opposed to war on principle, and those opposed out of fear for what might happen if America and Nazi Germany were to declare war on one another. That's why the Lend-Lease Act kind of circumnavigates the idea of war.

Nowadays, the Lend-Lease Act is seen as having been crucial to the defeat of the Nazis, and as such is considered an occasion when the U.S. Congress stepped up and answered the call of history.

Seriously; you only need to check out The Man in the High Castle to get an idea of what the world would have been like if Hitler & Co. had won. Hint: it's not pretty.