What he is in fact referring to is his own overarching view that the Constitution should provide socialist guarantees of redistribution of money from those who earn it to those who do not. That is his core economic philosophy, and that is his objection to the United States Constitution:
That is the "fundamental flaw that continues to this day" in the worldview of B.O.
He definitely favors redistribution of wealth, and said so in the other interview. That's also the one where he talks about the Warren court and overcoming constitutional restraints. All of that is abhorrent.
But this was a different interview, on a different subject. They were discussing the presence of slavery IN the Constituion, the way it was implied but never stated outright, in the 3/5ths clause, etc. He said that the Constitution REFLECTED a fundamental flaw--racism against blacks--and that that flaw continues to this day.
I'm trying to find a transcript to back up my point. I realize I'm peeing in the wind here, it's just that the other interview is substantive and relevant. This one, imo, is being distorted. Racism indeed continues to haunt us to this day. Not only in the ways he would suggest, but also in the reverse. We'd have been much better off without slavery, Jim Crow, etc. I don't think this discussion was about socialism at all.