[pandaman]

>I'm under the impression that to vote you must register in a voting district, surely that registration requires something like a birth certificate or a SSN

In California, at least, you can just use your state ID number and last four digits of your SSN [1]. California gives IDs to illegal aliens and SSNs are available to many non-citizens. These might have been checked for citizenship or might not. I suspect that they are not since the SSA itself wants you to bring the naturalization certificate if you want to change your non-citizen SSN card to a citizen's one. California never asked me for proof of citizenship so either it has an access to the citizenship data unavailable to the SSA or it just registers anyone with an SSN and a state ID.

1. https://registertovote.ca.gov/

[masonic]

CA has also sent voter registration cards to those known to not be citizens in the Real 8D era.