“We have many thousands of voter commitment cards, divided by precinct, and we know how many of these voters need to show up on caucus night to win even one or two delegates,” Mr. D’Alessandro said in an interview at the Sanders headquarters in Des Moines, as 20 volunteers called voters about events featuring the candidate. “That’s the ballgame: making sure enough people get to enough precincts.”

The Clinton campaign is also confident about its turnout goals, but Mr. Paul and his team have spent far more time building political operations in each precinct. Thousands of fliers have been sent to supporters providing the addresses of their caucus locations. And over two weekends this month, thousands of volunteers joined in dry runs of caucus-day operations at more than 150 Clinton campaign offices, union halls and homes across the state.

“Last summer, we got to the point of having a supporter in every precinct of the state much earlier than any campaign ever had, because of the tenacity of our organizers to drive from gravel road to gravel road to identify supporters,” Mr. Paul said. “Look, there are 1,681 precincts. You organize from there.”

A map of Iowa on Mr. Paul’s wall shows the 99 counties and different news media markets, with sticky notes marking planned trips for Mrs. Clinton, her husband and other surrogates. Mr. Paul carries a binder with a spreadsheet tracking Mrs. Clinton’s visits and crowds, and a laptop to review readouts from each event about the number of commitment cards collected and volunteers signed up — information he shares with her quickly.