Sometimes the candidate can be a circulator, but not everyone can be a circulator.
Most local campaigning election laws have specific requirements for the person who circulates the petition, even if it is the candidate himself.
On most petitions, there is a part for the circulator to fill out, also.
For example, after the circulator gets the signatures, he must certify at the end of the petition the number of signatures and that he witnessed each of the voters sign.
Sometimes this certification must also be notarized.
If the circulator's portion is incorrect, none of the signatures on that part of the petition will be valid.
Always check the requirements for circulators.
Even if the political campaign candidate's and the circulator's signatures are proper, some of the individual signatures might be declared invalid.
Many of the petition forms we have looked at have a space after the signer's address for the person's resident precinct.
This is to help the elections people when they check because they keep the list of registered voters' names by precinct.
In some areas, each part petition can only contain signatures from one precinct to make validation of the names easier.
In light of the fact that many elections offices are now fully computerized and names can be checked without reference to the voting precinct, these requirements are archaic, but they are still on the books and still used to trap the unwary.
Be sure to check if your state makes having the precinct mandatory, or whatever, because the signature will not be valid without it.