Your statement is illogical and nonsensical. In many states (and a growing number) you have to show proof of residency to vote. It’s not up to others to prove you are disqualified to vote.
The Constitution requires that you be born in the United States. Showing valid proof of that birth should be a basic requirement to run for that office, the same way you have to show proof of residency to vote.
In any event, those claiming he was born outside the U.S. have raised sufficient doubts about the validity of his purported “birth certificate.”
And did Bush or Clinton or Kerry have to do that? No, because there was no evidence suggesting that they weren't born in the U.S. And there is absolutely no evidence I am aware of, certainly none that has been shown here, to indicate that Obama was not born in the U.S. either. If he was born here then he's a natural born citizen and the case is closed. Where is the evidence he was not?