In any other context ...
I have no idea whether this will sink his candidacy or not. But I do know that Barack Obama is lying. In any other context, Obama would have no cover and no further credibility. You wouldn't accept such nonsense in your personal interactions. Why would you knowingly accept it from a Presidential candidate?
Geraldine Ferraro gently tells the truth, perhaps at the wrong time and place, and she's out. Barack Obama overtly lies and somehow it's our problem. Our ministers have all made similar statements and we didn't walk out. His mother was a bigot at times, as ours must have been too, but he loves her just the same. Our whole society is still too racist to understand Rev. Wright's message in the proper context. So what? Obama is lying just the same, on a very serious matter as regards the Presidency.
It's the second coming of Harold Hill. "When the man dances, certainly boys, what else? The piper pays him!"
And I would be careful about calling somebody a liar when he has said, and will say, so many different things in so many different ways that the truth is suffocated by the volume of fluff. I can even find a way I can believe his denials. See Freedom Dogs
In short, there is no profit in calling a slick politician a liar. Complain about their stated views, or the "inconsistency" between their views and votes, or their views one day versus the next. It's an "issues oriented" difference and there are LOTS of them and they're huge. We don't need the character argument when the candidate can make that point himself.