Huffington Post is clearly liberal. David Barton is an evangelical Christian minister who is a Texas Republican Politician. I imagine he is well versed in American history, but with his political activism, he clearly has a biased viewpoint. It seems less academic and more political in nature.
As for the 'expert' article: The quotes are sourced from secondary articles. As in there is no direct proof that the quotes are authentic or fabrications that have come about over the last 200 plus years. A simple google search for "David Barton Christian Nation" will show a lot of links that claim Barton has no real evidence of the quotes.
I don't see what's wrong with reading the Huffington Post for information about the founding fathers. Or watching Fox News for information on the economy, Obama's presidency, War, etc.