I feel that it is only out of the realm of possibility because we are able to review the outcome with the 20/20 vision of hindsight.
I think you would have to agree that Germany was intent on conquering and invading Britain. I can’t help but believe they were sure of their eventual success.
Being confident, why would they not start developing methods to take the “next step”? That being, the direct assault of the US.
I don’t see anything to indicate that they had any desire to take the war to the United States. Hitler did not want war with Britain. He believed, even quite late into the war that he could be friends with Britain, and that the war between them was insensible.