It is his memoir fer crissake. If he admitted it in his memoir, he admitted it, and you don't have to put in the disclaimer "according to his memoir..." It sounds like you are saying, "according to the tabloid press, he admitted..." Now I will grant his memoir the status of the tabloid press, but still, it is his own byline, and so we can take it as an admission and not a potentially false allegation by a third party, unless there are two BHOs.
Actually, from the recent press on his nationality and last name difficulties, there could be three HBOs, so it is a nice defense. I am not sure that having a multiple personality disorder is a good place to start one's bid for President, but it is an interesting strategy.
three HBOs.....
Hussein Barack Obama? Good one!