The guy must
be a time-traveler. His website says that his forthcoming book will be published in 2011.
As far as causality and such:
The bad news is that you are slipping through alternate realities continuously.
Remember when you couldn't find your keys the other day? You would swear that you left them right there on the kitchen counter, but they weren't there later. Things is you DId leave them right there on the kitchen counter. Somewhere between leaving the keys there and looking for them, you shifted to an alternate timeline where you actually left the keys over there on the end table next to the couch where you found them.
Just try to roll with this kind of thing, and don't think about it too much. And if you DO remember President Stevenson being elected back in '52, don't waste too much time trying to convince everyone else. they'll just think you're nuts.