Whenever I hear people wondering about these dark secrets of politicians, I ask myself the following, before I even look at the evidence. "How many people would have to be in on this secret whose careers would be destroyed if it were found out? Why, then, would they go along?" I recommend you start at the same place.
The Obama rumors and the Edwards rumors - not much cost for many people there. The Sarah Palin rumors - dozens of people would have to be putting their careers on the line for a brand-new governor.