According to Mother Jones, most of the attendees were Drake University students.
The queue stretched so far back that you couldn’t make out the end of it, and people waited in the cold for hours to get in (and many were ultimately turned away when the venue reached capacity). If Trump could muster this much support at a moment’s notice, you would think he should be well on his way to winning the Iowa caucuses. But on further inspection, the impressive crowd was composed largely of Drake University students, few of whom actually seemed prepared to caucus for Trump—or even to caucus at all.
“I’m just here cause I think he’s hilarious,” said one Drake student, who declined to give her name.
[ … ]
“We’ve had all these very serious events with random raffles and drawings, and then Trump shows up on campus and he gives out around 3,000 tickets on an app to an event happening in an auditorium that holds around 700 people.”