In IA you just have to be registered and I think you can register right up to the day of the caucus.
But that’s what Trump’s other issue is. Many people have been coming to his rallies. Apparently, they take down all attendees contact information (phone#/email#, etc), but they haven’t been getting back with the attendees to determine if their registered or would volunteer for the campaign.
Trump’s lagging in the small counties for precint captains. Most of the legwork done to register and get voters to volunteer takes place before Christmas. There is some extra time this cycle since the Caucus isn’t until February, but the groundwork needed to be done months ago.
The RuPaul bots are notorious in IA for hounding people to the caucus to the point you want to slap the sh!t out of them. There that annoying. And yet, not even they could get over 25% statewide and their organization was a machine, which relied heavily on new voters and left-leaning defense doves.
That’s why Trump is in trouble in IA.
I was running numbers in OH on the "early voting" in 2012 just as you are, with every bit the same certainty. Didn't work out that way at all.