In Virginia, when a person registers to vote, they must check YES/NO to the question "Are you a citizen?"
Merely submitting a registration application DOES NOT GET YOU REGISTERED TO VOTE.
Your name, address, date of birth, and social security number are run through several state and federal databases to check your citizenship, see if a death certificate has been issued for you, see if you are a convicted felon, see if you are already registered, and the like -- takes a few days.
Virginia has instituted "same-day registration" -- SDR -- you can register to vote at the polling place and cast a PROVISIONAL BALLOT. The provisional is placed in a sealed envelope, you sign it with identifying data, two election officials attest and sign, and the sealed ballot envelope goes to the local Electoral Board. The State then runs your registration application through the normal process. Eight days after the election, the state notifies localities if an SDR is good or bad. If it's good, you are registered and your provisional ballot is counted. If you don't pass any of the checks, your registration is denied and your provisional ballot is NOT COUNTED, but is stored with other election material in the local Circuit Court Clerk's vault for 2 years.
Since VA instituted SDR, there have been a few cases of people completing an SDR in one county, go to another county, do the same, etc. All these fools got an appointment with the State Police and the local Commonwealth's Attorney (state police have a small group that works only on election crimes).
Dumbass Republicans know this but nothing stops them from their usual stunts.