He's Southern, male, a Baby Boomer, and not an evangelical. It would be practically ASB not to.

Then there's the Rule of Reckless, otherwise known as the Ted Kennedy/Mark Sanford Rule: the more narrow escapes you have, the bigger risks you take until inevitably you're caught with increasingly high stakes and consequences.
If Edwards becomes President, and I don't think he would, I think we have to admit to a currently somewhat distasteful possibility. I apologize if to mention this is too soon, or if by chance any poster here was close to Mrs. Edwards, but she had cancer as early as 2004. In my mind, in a world where John Edwards is President, there is a chance, however remote, that the pressures involved in that could lead to an earlier death. If she passes away in 2005 or 2006, there's a very narrow time frame for the President to be "caught in a affair"
After the mourning period, John Edwards becomes "The Widower President" and he becomes free to pursue relationships with other women. If Edwards is dumb enough to get someone pregnant, that's a horse of a different color, but probably nothing that would lead to impeachment, though honestly I don't know how such a situation would play out.
Again I'm sorry if it's too soon to bring the scenario up, and I hope I don't sound like an unrepentant Edwards supporter.