Yes, there are claims that Obama may not a natural born citizen regardless of where he was born since his father was a Kenyan. I believe that he was born in Kenya. Thus, his mother was to young to pass along American citizenship. I have not heard evidence that Obama’s mother was in Hawaii preceding his birth.
If Obama attended Occidental College as a foreign student, that could indicate that he’s not a natural born citizen as well.
If Obama attended Occidental College as a foreign student (most likely Indonesian), that could very well indicate that he's not an American citizen at all!