We have to be especially careful about believing stuff we want to believe just because it confirms our bias.
I would be just as cautious about accepting one partisan book writer's word as another. The author of this anti-Obama book may be a bigger liar than Obama.
The grandfather detention story was told to Obama by his step-grandmother, and she repeated it herself to the media. So that is not a Barack Obama lie. You can't blame a man for believing what his grandma told him.
The other stuff, I will not just take the word of someone I have never heard of. Whether his name is Obama or Maraniss.