The Constitution says otherwise, assuming that he is not eligible.
No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States.
Not eligible == can not be President. Elections aside, votes aside, politics aside. You have to be eligible, or you are not President.