Even as former President Donald J. Trump faces a crowded field of Republican primary challengers, he has kept a relatively light campaign schedule, particularly in Iowa, the first state to hold a nominating contest in the 2024 election.

But with less than four months until Iowa’s caucuses, Mr. Trump and his team on Wednesday began a more concerted effort to lock up his support there, starting with two events in eastern Iowa — the first of five planned visits to the state over the next six weeks.

The increased pace of Mr. Trump’s Iowa trips, along with a six-figure advertising purchase by a super PAC supporting him, suggest a stronger push by his campaign and supporters to shut down his rivals before any can pose a threat.

Speaking at a “commit to caucus” event in Maquoketa, Mr. Trump said he hoped to improve on his showing in Iowa in 2016, when he was the runner-up to Senator Ted Cruz of Texas.

“We’re asking for a commitment,” Mr. Trump told the crowd. “Everybody do whatever they can. Get three people at a minimum and come out, bring them with you.”

With Mr. Trump holding a commanding lead among Republicans both in national surveys and in Iowa polls, some rivals have made barnstorming the state a cornerstone of their strategies, hoping a victory there could help them coalesce support in later primaries.

For Mr. Trump, winning Iowa next year could hinder any of his challengers from building the momentum required to knock him off his perch as the Republican front-runner.

Mr. Trump’s Wednesday visit was just his eighth trip to Iowa this year, far fewer than the other candidates have made. Gov. Ron DeSantis of Florida, who frequently polls as Mr. Trump’s strongest rival, has made Iowa a particular focal point, planning to visit all 99 of its counties and building a robust state operation.

Yet even as an Emerson College poll released last week showed Mr. Trump’s support among Iowa Republican voters slipping somewhat over the past four months, he still remained 35 percentage points ahead of Mr. DeSantis.

“They’re losing in Iowa by like 35, 40 points,” Mr. Trump said of his rivals. “You know, second, Ron DeSanctimonious,” he added, referring to Mr. DeSantis before criticizing his efforts to kill the Renewable Fuel Standard, which requires ethanol to be blended into the nation’s fuel supply, a boon to Iowa’s economy.

Mr. Trump also emphasized that he was committed to Iowa, despite his sparse visits so far.

“With your vote in January, I’ll fight like no one else, and it’s very important,” he said. “It’s so important, and it’s so important that you are first, because I believe in this state very much, and I believe in the people.”

Becky Hauder of Dubuque, who caucused for Mr. Trump in 2016, rejected the idea that he had not campaigned in Iowa enough to win over voters.

“He’s here today,” Ms. Hauder, 55, said as she stood in line awaiting Mr. Trump’s first event in Maquoketa. “And I know he’ll be back. I know Iowa is very important, and he’s always come here in the past.”

The event in Maquoketa was a more traditional Iowa campaign event, with a crowd of hundreds assembled in a more intimate setting than Mr. Trump’s enormous arena rallies. Unlike at those rallies, Mr. Trump took questions from his supporters.

The gathering reflected the Trump campaign’s renewed push to convert the former president’s popularity to in-person support in January. Mr. Trump said in 2016 that his campaign’s ground game was weak, and supporters have raised similar concerns this year.

Local politicians educated the crowd on the particulars of Iowa’s quirky caucus process. Campaign staff and volunteers urged the audience to sign cards pledging to back Mr. Trump in the caucuses. (Mr. Trump’s campaign has said it has collected more than 27,000 such cards so far.)

Mr. Trump’s campaign has planned at least two similar events, a frequent feature of the Iowa campaigning process, in the next month. Yet he has eschewed other traditional Iowa events, including large multicandidate ones like a major gathering of evangelical Christians that was held on Saturday.

Mr. Trump has remained popular with evangelical voters, even as he has expressed views that might normally alienate them. The former president, whose appointments to the Supreme Court paved the way for the overturning of Roe v. Wade, has been noncommittal on endorsing a federal abortion ban.

During an NBC interview broadcast on Sunday, Mr. Trump criticized Mr. DeSantis for signing a six-week abortion ban, calling it a “terrible thing.” On Tuesday, Iowa’s Republican governor, Kim Reynolds, who has signed a similar law, attacked Mr. Trump’s comments.

The speakers at the event in Maquoketa emphasized Mr. Trump’s role in overturning Roe. Bobby Kaufmann, a Republican state representative who is advising the Trump campaign, said Mr. Trump was “the most pro-life president” in American history. “It’s not even close,” he added.

Tim Nichols, a voter from Clinton, Iowa, said that he supported his state’s ban, which conservatives often call a “heartbeat” law. But he added that he understood Mr. Trump’s stance on the issue.

“This is a heartbeat state, and I don’t think we should back up from that,” Mr. Nichols said. “But at the same time, it is still a states’ rights issue.”

Mr. Trump was also set to give a speech on Wednesday afternoon at a convention center in Dubuque, where his campaign expected a crowd of thousands.

The speeches coincide with increased spending on advertising by MAGA Inc., the super PAC backing his campaign. The group spent more than $700,000 on ads in Iowa last week and this week, according to AdImpact, a media tracking firm.

Similar groups backing Mr. DeSantis and Nikki Haley, the former South Carolina governor and former United Nations ambassador, each spent more than a million in the same period.

Nicholas Nehamas contributed reporting from Miami.