By the time the doors opened Sunday morning, the line to enter former President Donald J. Trump’s caucus organizing event in Ottumwa, Iowa, snaked down the sidewalk and around the parking lot.
The hundreds of people who stood outside an event center in this small city, sweating through their “Make America Great Again” hats and their mug shot T-shirts, were happy to be here — the wait and the weather, near 90 degrees, be damned.
“Hey, I’ve got Newsmax,” a volunteer in a Trump 2024 shirt called out, pointing to a camera apparently from the conservative cable network. “How about we start a ‘Let’s Go Brandon’?” he suggested, referring to a chant understood to be code for an insult to President Biden.
From their perches on the sidewalk or nearby grassy knolls, Mr. Trump’s supporters obliged.
Onstage later, Mr. Trump characterized his political opponents as “very bad people” and said that Republicans were generally nicer.
“But please don’t be nice,” Mr. Trump told a crowd of well over 1,000 people who filled every available seat and packed a hall at the Bridge View Center. “Don’t be nice, because if we don’t win this election, we’re not going to have a country anymore.”
Sunday’s “commit to caucus” event was part of the Trump campaign’s push that began last month to ensure that the former president’s foothold on the Republican Party translates to a strong showing at the Iowa caucuses in January. Such a victory could more definitively shut out his rivals and clear a path to the nomination.
This pocket of southeastern Iowa, Wapello County, is of particular significance to his campaign. Democrats had won it in 10 straight presidential elections until Mr. Trump flipped the county in 2016 and held onto his advantage four years later.
Even after his loss in 2020 — or maybe because of it — Mr. Trump has retained his appeal here. In remarks from the stage, Jeff Kaufmann, chairman of the Republican Party of Iowa, celebrated Ottumwa as “a place that used to be blue, and now you’re dark red, like the rest of Iowa.”
Robert LaPoint, 61, said that he was among those swayed to reconsider past support for the Democratic Party. Though he had long identified as a Democrat, he said, he began to feel that the party had drifted too far left on issues like abortion. As of four years ago, he said, he had no party affiliation at all.
It was not just the party that had changed, he added. In 2012, when Mr. LaPoint was still a Democrat, he met Mr. Biden, who visited Ottumwa while campaigning as former President Barack Obama’s running mate.
“The Joe Biden we have now is not the Joe Biden we had then,” he said, pointing to Mr. Biden’s values and alluding to some verbal and physical stumbles that Republicans have suggested made Mr. Biden unfit for office.
Mr. Trump criticized Mr. Biden extensively in his remarks, which lasted about an hour and 15 minutes. But he also reserved some time to criticize his Republican rivals, even as he holds a commanding lead over them in national and Iowa polls.
As he often does, Mr. Trump railed against Gov. Ron DeSantis of Florida, who generally polls behind Mr. Trump and has been viewed as the former president’s chief rival.
Mr. Trump also attacked Nikki Haley, whom he once appointed ambassador to the United Nations, and who has built momentum after breakout performances at the two Republican debates. “I call her birdbrain,” Mr. Trump said.
Mr. DeSantis, Ms. Haley and other challengers are banking on the state’s tradition of retail politicking, with smaller gatherings across the state. Mr. Trump’s schedule in the state has been lighter. But he draws sizably larger — and significantly more devoted — audiences.
When he appears in Iowa, Mr. Trump is quick to tailor his national messaging to the state’s concerns and to frame a victory in the caucuses — and eventually the general election — as a dire necessity for a state in which he is hugely popular.
Iowa is a major producer of ethanol, and Mr. Trump told the crowd that if Mr. Biden were to win again in 2024, “gas-powered cars will be gone, Iowa ethanol will be totally destroyed, and the economy of this state will be devastated.”
Mr. Trump also cast himself as a defender of Iowa’s farmers, later meeting with a group of them.
Though Mr. Trump again denounced the criminal indictments against him, he did not explicitly mention the civil trial set to begin on Monday in the New York attorney general’s case accusing the former president and his family business of fraud. Mr. Trump’s campaign sent out fund-raising appeals this weekend referring to the trial.