Also, as to how you "prove" citizenship, other than a passport -- a certificate of birth in the US, if genuine, proves citizenship, but only under an interpretation of the Fourteenth samendment that some reject. Otherwise, you've got to get into your ancestry. For example, Geroge Romney, who ran for the GOP nomination in 1968 and was Gov. of Michigan, was born in Mexico, of American parents fleeing persecution of polygamists -- so even if he had a birth certificate, it would have shown Mexico, although his american parentage would make him a citizen by a statute that I don't think anyone challenges.
If you are in that type of position, you have to have a long and interesting conversation with the State Dept. to get a passport.
Your skepticism eminently qualifies you for a post on the RNC. Just as a heads up, the Mayor of Detroit admitted to 150,000 phony registrations in his fair city alone.
If there are not at least 500,000 falsely registered illegal aliens in California, I'll drive each one of the bastards back to his country of origin and buy him a drink on the way.