Oh, they know. They are lying burlap bags full of crap though, and will argue till they are blue in the face that since not every single one of the founding fathers was a Richard Dawkins type atheist, they must have been all been Christians who hated abortion and faggots.
No they don't, or theey do and ignore it. The far religious right focuses in on on a few small groups early in history that migrated to the US, fleeing from people who considered their religious practices aberrant, and holds them up as the founders of america. Of course the group in question would consider most modern christians aberrant, including the religious right and the mega-churches.