Because Obama was adopted by an Indonesian and attained Indonesian dual citizenship and never renounced it, he can't be President.
Now, because he didn't say the oath properly, he can't be President?
I guess that would make Obama the most illegitimate President in history.
First one may or may not be true, but, if true, then he can’t be president.
Second one is probably true, but it would not disqualify him from the presidency.
Third one would only incapacitate him from performing the duties of president, not prohibit him from becoming president, and in any event would be easy to fix (by taking the oath again).