The link takes you to the PDF of the Obama campaign's response to that new book by Jerome Corsi. As a critique, it is very well done, which is also its weakness.
It is unfortunate that such an exhaustive PDF response is necessary to counter what amounts to a crack pot with a publishing deal. I wonder how many hours of work went into the response that could have been better served on other topics, but the current state of American politics demands such. I also wonder how many people will actually read the critique, as it can get wonkish, nitpicky and isn't as exciting as one would expect. (Which also tells me the tone of Corsi's book - probably only 'exciting' to folks who like to see their views validated in print.)
Politically, I think this book fiasco is a wash. The lunatic fringe of the right wing* is who this book is being marketed to, and it isn't like a lot of those folks are going to read this book and suddenly go from Obama supporters to Obama detractors. Ditto with right wing radio and most of their blogosphere. None of these folks were considering voting for Obama in the first place. All it does is validate some crazy opinions out there in the fringe where chain emails are considered footnotable sources.
All over the left, the more important point is to respond to this nonsense. It is the only choice, as we saw what happened when Kerry ignored his critics. Some lefties will use this as their geas for the next 8 - 12 months, proving again that there are enough folks out there who are just on my side of the aisle solely to disagree and not make things better. At some point, the response will go too far, and give way to the next fringe issue in this election.
Who wins? Publishers and media: since they're the ones making money off of this. While the media has been able to effectively and quickly debunk this book, as have campaign operatives for Obama, just by them debunking this crack-pot lends him credibility in some circles of the right. Remember, the right's current election narrative depends on the press supporting Obama a little too enthusiastically. Going after this book only helps that.
On the other hand, it is yet another opportunity to expose the myths promoted by chain emails and books like this about Obama. Every time I read stuff like this, his story becomes more uniquely American, the kind of journey that can only happen in our country and our culture. I can only believe that such exposure will only help the Obama campaign in the center - which is where the election will be won.
* (The lunatic fringe is Not to be confused with right wingers or conservatives who don't support Obama based on real policy reasons, where the presidential debate should be directed.)