Apparently History has been changed since I was taught in the 50's and 60's.Operation Sea Lion was cancelled simply because The Germans lacked the superiority of our air and sea. They did not hold our skies and they did not hold our waters both of which they needed to control for a successful invasion of Britain. It had nothing to do with America entering the war.
My apologies to Great Briton for not being aware that they single handedly kept the Nazis at bay in the 40"s.