Ed Flanders as Truman

I wonder why Ed Flanders didn't portray Truman in this series, as he has best portrayed Truman than any other actor? He steals the latter half of the Gregory Peck movie MacArthur, with his riveting performance as Truman.

Here in this movie Harry Morgam plays Truman. I guess you could do a lot worse than Morgan, but I wonder was the possibilty discussed to cast Flanders in the role? Or, did Flanders turn it down?

He had already played it so often that type casting would not have been the issue.