David Barton is a self-proclaimed historian, founder of WallBuilders, and darling of the Religious Right. He has written many books, such as The Jefferson Lies: Exposing the Myths You’ve Always Believed About Thomas Jefferson (co-written with Glenn Beck); Separation of Church & State: What the Founders Meant; and similar titles. His ideas have been widely attacked by the “academic elite”, which basically says he is full of hooey.
I’m not going to start listing his assertions and the counters from the mainstream of constitutional scholars and historians. Barton is prolific, and life is short. I suggest, rather, that you check out the WallBuilders’ site, look for his name in the papers, and keep an eye on what happens with the Texas schoolbooks.