WATERLOO, Iowa — Right off the highway in the tiny town of Waterloo, Iowa, a flashy neon sign welcomes passersby to the Electric Park Ballroom — a cream-colored building with flamingo-pink awnings that looks more like a bowling alley than a ballroom — for weddings, parties and on this night, the “Annual Republican Dinner.”

The dinner typically attracts fewer than 100 people but this year, there will be at least that many national reporters coming to the event. Nearly 300 people have bought tickets to the sold-out dinner and dozens more are expected to show up for a $20 ticket just to get in the door.