WAUKEE, Iowa — The Republican Party belongs to President Trump, and everyone in the Waukee Elementary School gymnasium knew it. Even the man who was ostensibly trying to persuade his neighbors otherwise.

“I want to explain to you why I, I — you might be surprised to see someone supporting Joe Walsh in front of all these Trump fans — and why I have the bravery that I do,” Jim Marwedel, 50, said nervously. “It’s because of my fifth great-grandfather, William Lee. He came from Ireland to the colonies and fought in the Revolutionary War. He was left for dead at the Battle of Guilford County, and I figured if he has the bravery to come forward and die for his country, I can just stand before you and talk about the Constitution for a few minutes.”

It did take some courage to do what Mr. Marwedel and a very small minority of Republicans did on Monday night when they registered protest votes against Mr. Trump — even if it wasn’t exactly the kind of courage required on a real field of battle. Mr. Trump’s true believers dominated school gyms, churches and other caucus sites across Iowa and helped deliver his first victory on the path to reclaiming the nomination of a political party that four years ago broke into civil war over his insurgent candidacy.

Some 140 miles away, when the caucus captain at the Butcher Block Steakhouse in Cedar Rapids called out to two men standing in the very back of the room — the only two who had not raised their hands to support Mr. Trump — there was a very pregnant pause.