What this program is based on, which is how could things have possibly turned out if Britain fell is interesting, but if they really wanted to make it good it would have been about the potential outcome had Russia fallen. The US would then have been forced to put a large bulk of its resources into Alaska to counter Hitler from that side. It may have even been forced to invade Russia from the east to keep Hitler from getting too close to the US. Then I would say until this country got its hands on the bomb it would have had its work cut out for it, and who knows if Hitler might have beaten the US at getting the bomb at that point, the resources at his disposal would have been infinite.
As long Hitler remained confined to Europe however and out of range of US targets, there was no doubt what the outcome would be, a US victory. Germany could not compete with the US economically and industrially. For every plane they could produce, the US could manufacture 10 or more. Same with bullets and tanks. And the US had twice the number of men. He didn't have a chance against the US with those odds, and his generals knew it.