Lilo,
I think that most of these politicians that get caught is not because they're stupid. I think it's arrogance, plain and simple. They have so bought into their own sense of power that they believe that there is no way they can get caught.

In my former life, I had to deal with politicians all the time. Whenever we gave a luncheon or dinner, we would always make sure to recognize the elected officials in the audience. If, God forbid, we missed someone who came in late or something, you cannot believe the phone call we would get afterwards! Ego, ego, ego.