As I already referenced in another response to LS, you can start with Hofstadter who points out Fitzhugh's fringe nature in his chapter on The Lincoln.
You should tap some of that into the thread. You're about to get the stand watie veracity award.
Walt
Not that you'd have any interest in it considering your tendency to IGNORE what you don't want to hear. I'll have to go get the book at the library, but its in the Lincoln chapter of Richard Hofstadter's "The American Political Tradition" (1948).