Bo, I do appreciate the explanation, although I was aware of those facts before I read your post (I have a bit of a background in history). I don't quite agree with your argument, though, that it doesn't say anything about them. If everyone murdered their way to the presidency, you wouldn't say, Well, that's politics! You would consider presidents the way I consider slaveholders: at best, flawed men unable to overcome the evil of the world in which they live.
But for our purposes, you more importantly misunderstand the point I was making in objecting to Gunfighter's use of James K. Polk, who was in addition to a slaveholder but a warmongering tool of the slave power who, despite claims that he represents some ideal of small government or minority rights, ran roughshod over them as he made the central government more powerful.
Polk is a bad example of protecting minority rights. So, for that matter, is the Constitution, at least to a degree. In my more cynical moments I agree with Lysander Spooner, damning the Constitution either because it proved unable to stop slavery or it actively allowed it, either of which make its usefulness and merit unclear.