I looked at the website and sorry, I don't mean any disrespect, but it seems pretty unfeasible to me. The current US population comes from all over the world and I wrote a hub on British DNA ("Who Do the British Think they Are?") and they definitely aren't Jewish. (apart from the ones who actually are Jewish, of course:))
Over the centuries myths like this have been developed to give countries and populations status in the mythological belief structure that they have accepted. For instance, there was an old legend that Britain was founded by a King called Brutus of Troy. This is of course total nonsense but it tied Britain in with the Ancient Classical cultures that were admired. Similarly, several populations have claimed to be the lost 12th tribe of Israel, even though they were not even from a semitic race.
What I find interesting is that many peoples have abandoned their own religions, their own beliefs and even their own history to follow the history of the Jewish people instead. Yet often those same people are anti-semitic. Go figure.