If the candidate has a penis.

Sounds like satire, but it isn’t.

They don’t call Arizona the “meth lab of Democracy” for nothing — where else could a lack of foreskin prove citizenship?

The Arizona Senate formally passed the “Birther Bill” today, but not in its original version.

Apparently, requiring presidential candidates to provide a long-form birth certificate before allowing their names on the ballot in Arizona — despite it already being a federal requirement to run for president — was a bit too much for a few GOP lawmakers. So they made some amendments: if you can’t find your birth certificate, and you have a penis, a document describing your lack foreskin will suffice.

[…]

To be accurate, that would be one of two documents from a list of options that would substitute for “the long form”. Here is a link to the amended bill.
The pertinent parts are in all-caps blue font. Purple Comic Sans would have been better, but what can you do.