Because her father was Janet Reno.
That joke — I hope you’ve stopped laughing by now — was brought to you courtesy of the man of honor and integrity, Senator Straight Talk himself. He told it at a Republican fund-raiser in 1998. Apparently the mainstream press mostly referred to it only indirectly; it was “too vicious to print,” according to the Washington Post.
I only learned of it from this hit-piece about McCain by Ronald Kessler on NewsMax, the wingnut news service. The Chelsea Clinton story seems to be well documented elsewhere; I can’t vouch for any of Kessler’s other allegations. But Kessler provides some good leads for anyone starting out doing oppo research on McCain.
The joke alone, it seems to me, should be enough to convince you that McCain is a fundamentally bad human being. It would be hard to work more viciousness and bigotry into two sentences.