The following states mail a ballot to every single registered voter: California, Colorado, Hawaii, Nevada, New Jersey, Oregon, Utah, Vermont, Washington, Washington, DC. Most other states have voting by mail, but they are absentee ballots and require that the voter request the ballot.
Picture that you are a nurse’s aid working in a nursing home. You are responsible for the care of 200 patients with dementia. You have access to their names, dates of birth, and social security numbers. You register them to vote on the state website, and list the nursing home’s address as their home. You know, to help your residents vote. It’s their right, after all.
The ballots arrive by mail. You fill them out and mail them in. They all voted a straight Democrat ticket.
In the unlikely event that it is ever investigated, there isn’t a single one of them that can testify against you. They won’t remember a thing, at least not well enough to ever prove anything.
This is how the “register online” and “vote by mail” systems are ripe for voter fraud.