Barack Obama, according to Article II, Section I, Clause 5 of the U. S. Constitution, is an illegal President. The law requires a candidate for the Presidency to be a "natural born citizen," that is, a second generation American, a U.S. citizen, whose parents were also U.S. citizens at the time of the candidate's birth.
Obama's father was a citizen of Kenya and a British subject at the time of his birth, which made him forever ineligible for the Presidency. For the same reason, Florida Republican Senator Marco Rubio is ineligible for the Presidency and Vice Presidency because his parents were Cuban citizens, not U.S. citizens at the time of his birth.
There is no ambiguity, although those who wish to undermine the Constitution would like the American people to think otherwise.