At an Iowa rally of 2,300 evangelical Christians for Senator Ted Cruz last week, Mr. Cruz’s campaign manager, Jeff Roe, said he would rather have those supporters, who were committed to a family values “movement,” than the thousands more who turn out at a Trump rally to be “part of a show.”

To persuade a new wave of caucusgoers to participate, Mr. Trump would have to defy the past. Only about one in five registered Republicans have attended past caucuses; the dream of bringing in thousands of marginal voters and increasing the turnout beyond about 120,000 Republicans has eluded many past efforts.

“The entertainment value of a Trump event is high, but the reality of his issues is a real challenge to him,” said Steve Grubbs, the director for Senator Rand Paul’s Iowa campaign, citing Mr. Trump’s past support for gun restrictions and abortion rights. “At the end of the day, you can like the concept of Donald Trump, but voting for him at the caucuses will be a lot tougher for people.”

And yet, despite his flamboyant politics and a strategy that seems focused on appearing, every hour of every day, in the national spotlight, Mr. Trump has put in place a robust field operation in Iowa, grounded in the most time-proven methods.

He was the only candidate of 17 Republicans to plant a volunteer for all 11 days of the Iowa State Fair at the state Republican Party booth this month. Even as Mr. Trump’s bravura flyby of the fair in a helicopter produced headlines, his little-noticed volunteers collected hundreds of cards with voters’ email addresses, providing invaluable contact data to activate more volunteers. It was a far cry from the early days of his campaign, when actors were reportedly hired to fill out the crowd when he announced his presidential run.

In Ms. Goertz, a motivational speaker, Mr. Trump has a political newcomer helping to lead his organizing in Iowa, but his state director, Mr. Laudner, is a 30-year veteran of Iowa campaigns. He has built one of the largest field teams of any Republican candidate this year: 10 paid staff members.