If Obama is not legally qualified to occupy the White House are any Bills signed by him (eg Obamacare)valid?
Yes, because he holds the office regardless of his validity, and he was put in the here by the electoral College. According to Levin, the only way to remove a president (and he is president, regardless of legal requirements) is impeachment. The high crime could be (this is me speaking, not Levin) swearing a false oath at some point about his eligibility.