"Real" father? A person's real father is the one who sat up nights with them when they were sick, who took them to school, who was complicit in their shenanigans. A girl's real father is the one who walked her down the aisle. Even if Bill Clinton hadn't done these things, his name is on her birth certificate. If any other man has any genetic connection to Chelsea, it's as sperm donor plain and simple, not as a "real" father.
Chelsea looks more like Hillary, but she looks like Bill too. Yes, I've read where Bill supposedly said someone else was her genetic antecedent; however, do you really think Bill and his ego would have admitted that even if it had been true?
At least one woman who accused Bill of rape also stated he had a certain physical condition that was very identifiable. Over the years I've seen it said by lay people that it would prevent him from fathering a child, but that simply isn't true.
According to you, Dire, adopted children don't have "real" parents. I never before thought you were that shallow.