LOL! I can't blame you for believing that - it's something we were all brainwashed by our public education to accept as a 'fact'.
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The point is, applying for citizenship is not enough. Until they ARE citizens they cannot pass their citizenship to their offspring.
That's how natural-borns are made - they inherit their citizenship from their parents.
No parental citizenship means NO NATURAL-BORN OFFSPRING.
The fact they had begun the process of naturalization is irrelevant.
[Wong Kim Ark's parents had begun the naturalization process as well, but the USSC still considered him to be native born, not natural born]
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“[I] find no fault with the introductory clause, which is simply declaratory of what is written in the Constitution, that every human being born within the jurisdiction of the United States of parents not owing allegiance to any foreign sovereignty is, in the language of your Constitution itself, a natural born citizen. . . . ” —
John A. Bingham, (R-Ohio) US Congressman, March 9, 1866 Cong. Globe, 39th, 1st Sess., 1291 (1866), Sec. 1992 of U.S. Revised Statutes (1866).
Citizenship is an absolute. There are no exceptions for a quasi state of 'almost' a citizen.
Rubio is not eligible for public office for the same reason Soetoro is not....and I will not be a hypocrite and say otherwise just because he is 'one of ours'!