The Constitution does not provide for either. It does provide for vacancies in the office of President. Most of those provisions speak of the removal of the President, or the death of the President. But if a person never qualified, and so was never legally President, it's a slightly different situation. By a combination of Section 3 of amendment XX and amendment XII, plus a bit of "English', a likely outcome would be for the House to pick a new President, from among the top three eligible electoral vote getters, per the That would be McCain, McCain and McCain. :)
But it that were to happen, McCain is challenge-able as well, not having been born in the US, but rather on the Coco Solo naval base in the Panama canal zone, where his father was the exec on a sub. (Some say he was born in Colon panama, which would definitely make him not Natural Born, and even being born on a US Naval base outside the US is questionable (although the base and the canal zone were under US control at the time).
What would happen if Obama is affirmed a usurper and must be removed from office? (Probably by the military under orders from the Supreme Court - just as in Honduras.)
Precedence was set in the U.S. Senate when two elected Senators were discovered to be foreign nationals, not U.S. citizens. Those elections were declared VOID - struck from the records as though they had never occurred and new elections were held. It should be expected that this will set precedence in this case.
If it happens with Obama I presume that the Houses of Congress will vote for a new President. God help us!
This could be dicey as the Democratic Party chiefs in both houses were involved with the Obama candidacy and knew about his ineligibility (Pelosi filled out paperwork for Obama as the Decmocratic Party’s candidate. She left out the part about eligibility verification - she is toast if she knew beforehand that he was ineligible! It means prison time.)
As for Senator John McCain; he was born in a public hospital in the city of Colon, Republic of Panama, three years before the U.S Navy Hospital would be built.
He is a citizen by statute as his parents were both U.S. citizens and he was born abroad (jus sanguinis).
He is not a natural born citizen, as he was not born in the U.S.A. to citizen parents.
Oddly enough when the Constitution was first written there was an inclusion (1790) allowing children born overseas to U.S. citizen parents to be considered natural born citizens, but it was repealed by 1795.
I hope this helps clear any confusion you both might have on this subject.
Natural born citizenship established by natural law is not found in any legal statutes concerning citizenship. It is the only type of citizenship that cannot be conferred by law, only by birth. This concept was very familiar to our founders.