The "greatest theologian" - Lincoln?

In the current issue of First Things, author Andrew Ferguson explores Lincoln's religion and summarizes with a quote from David Donald, something like "I have no idea."

Over at HNN Lincoln author Vernon Burton asks if Lincoln was not "the greatest theologian of the 19th century..." meanwhile he has a formum with no posts.

If this is supposed to be one of those refreshing debates on Lincoln that will characterize the bicentennial, let's connect the debaters.