[katana]

Sorry to say, but I think your assumption is wrong. There were plenty of Americans at the time, including Joe Kennedy and Charles Lindberg, who firmly believed the British were doomed and that America had no business saving them. Roosevelt was sympathetic to the British plight and did everything he could within (and a bit beyond) what the neutrality laws would allow to help them, but we fought Hitler because he declared war on us.

[SoDak]

I think common sense and a sense of imminent doom would have convinced more than enough of congress at the time to do the right thing.