Where does it say in the Constitution the President can be a citizen?
A silly question. Article II
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.
Now, where did it say that "“Posterity” and “natural born” are pretty much means the same thing"?