The series was an abortive attempt to create an Americanised Blackadder knockoff.
Note that this theory is based pretty much entirely on Brad Jones's DVD-R Hell episode on this, so I'm doubtless missing a lot of context (both in the show and American TV in general), but I was struck by the show's similarities to Blackadder, especially the third series wherein Edmund is the butler of the dimwitted Prince Regent, much as Pfeiffer is the butler to a goofy Abraham Lincoln. There are a number of direct equivalents: irreverent historical setting, caricatures of historical figures, zany schemes - Pfeiffer even has his own Baldrick tagging along after him.Desmond Pfeiffer is an Unreliable Narrator
The entire series is his personal diary, and all the various historical character's being portrayed as dimwits is the way he sees them. Note the one who insists that the story is entirely true, Desmond Pfeiffer himself.