Where would the bombers take off from and go back to?

The US was very much isolated from German and Japanese air forces.

Then add in the long distance from the coasts to some of the large industrial centers like Detroit and Chicago.

As it is, Amsterdam to NYC is a 7200 miles round trip. That has you flying over the UK, however. German pilots would have needed a longer route.

Edit: As a comparison, round trip from Midway Island to Tokyo is only about 5100 miles.