Anybody can go to the Board of Elections and purchase a disk with the name, address, birthdate, and history of voting of each registered in the county. By history of voting, I mean which elections the voter has cast a ballot, not who the voter has cast a ballot for. You can easily assign possible preferences for a voter by seeing whether they voted in contested Democratic primaries and/or if their precinct consistently votes in overwhelming numbers for Democrats.
Once a list is compiled, the prospective cager could put together a cheap mailer asking the voter to return the card if they want to stay registered, and if they do not, or if the cards come back undeliverable, the voter is added to a list of people who will be challenged at the polls. As Adam notes in his post, being challenged could keep people from casting their ballots, or at least being forced to cast provisional ballots which generally aren’t counted. And wrangling over ballots tends to create long lines at the polls which further discourage people who aren’t even challenged from casting their ballot, as voters often don’t have a whole lot of time away from their job to wait in line to vote.
So yeah, a systematic voter caging effort could easily be put in place and steal the election, especially a lower turnout election like the midterms. We already know that the Ed Martin campaign is planning an aggressive poll watcher program. That’s his right, as long as it doesn’t cross over into an effort to obstruct people from lawfully casting their ballot.
Fortunately, it’s not as if voter caging is unstoppable. Parties can send trained people, usually lawyers, to the polls to observe and report back to headquarters about possible voter intimidation practices, and also to provide immediate guidance to voters as to their rights.
I have a couple of calls out to see what the Missouri Democratic Party is preparing to combat possible voter caging. I’ll report back when I get some info.