Second vote for Morgan Freeman. I’d vote for him as God, too (Bruce Almighty). I know he’s an actor, but he just sounds so convincing. I’d like to be convinced by my president–which hasn’t happened in my (long but faded) memory.
Hmmm, not much of a list: No Walter Huston (Gabriel Over the White House), Frederic March (Seven Days in May) or (my vote) Henry Fonda (Fail-Safe). Of those listed, I’d probably vote for Freeman too.