Native born isn't really the issue. It is pretty easy to argue he isn't native born if you just look at the original constitution. But the 14th amendment pretty much states that if you a citizen you have full rights whether naturalized or born, and of course anyone born in the country is a citizen. This means the whole native born stuff is meaningless now. By the time this amendment was passed the country no-longer worried that England might infiltrate the government and put an Englishman in charge and there was the very real problem of the Southern states abridging the rights of blacks.
If he is a citizen he can run for president, under the law of the land at the time all he had to do to naturalize was file a short form stating that his mother was a US citizen. My mother filed this form on my behalf when I was a child and I got a nice letter from Jimmy Carter. Same with McCain, he was probably born in a hospital outside the canal zone, but it doesn't matter due to the 14th amendment. He is unquestionably a citizen.