That can't be it. You are allowed to lie and cheat if it is about sex - if you are a democrat at least.
Not when you are just a candidate. The difference with clinton is he was IN the WH.
And to expound on my candidate vs. office holder observation: Note the Gennifer Flowers story almost did in fact knock Clinton out until Don Hewitt helped with the Sixty Minutes "Stand by my man" business. The story was characterized as ancient history, two prong attack included tapes being doctored, and the implicit promise to "not do it again".
This may or may ruin Kerry, but the idea it is widely accepted and yawned at is nonsense.