Decrying a Republican “culture of losing,” Governor DeSantis sought Saturday to weaken President Trump’s grip on the GOP as tornado warnings interrupted a collision of leading presidential prospects in battleground Iowa.

Mr. DeSantis, expected to announce his 2024 presidential campaign any day, briefly flipped burgers and pork chops at an afternoon picnic fundraiser in Sioux Center that drew hundreds of conservatives to the northwest corner of the state. From the podium, the 44-year-old governor highlighted his eagerness to embrace conservative cultural fights and sprinkled his remarks with indirect jabs at Mr. Trump.

“Governing is not about entertaining. Governing is not about building a brand or talking on social media and virtue signaling,” said Mr. DeSantis, who wore a blue button-down shirt without a tie or jacket. “It’s ultimately about winning and producing results.”

Mr. Trump, a candidate since November, had hoped to demonstrate his political strength with a large outdoor rally in Des Moines, the capital, later in the day. He canceled the appearance hours before its scheduled start time due to a tornado warning.

Roughly 200 supporters had already gathered at the venue. “I feel like it’s still Trump’s time,” said Robert Bushard, 76, who said he drove about four hours from St. Paul, Minnesota to see the former president. Of Mr. DeSantis, he said, “He’d be a good president after Trump.”

Republican primary voters across the nation are sizing up Messrs. DeSantis and Trump, two Republican powerhouses who are among a half dozen GOP candidates already in the race or expected to announce imminently. Mr. Trump is well ahead of his rivals in early national polls, while Mr. DeSantis is viewed widely as the strongest potential challenger.

Mr. Trump was hoping to return to the comfort of the campaign stage after a tumultuous week.

On Tuesday, a civil jury in New York found him liable for sexually abusing and defaming advice columnist E. Jean Carroll and awarded her $5 million. A day later, during a contentious CNN town hall, he repeatedly insulted Ms. Carroll, reasserted lies about his 2020 election loss and minimized the violence at the U.S. Capitol on January 6, 2021.

Mr. DeSantis has burnished his reputation as a conservative governor willing to push hard for conservative policies and even take on a political fight with Disney, which he highlighted in Sioux Center. But so far, he hasn’t shown the same zest for taking on Mr. Trump, who has been almost singularly focused on tearing down Mr. DeSantis for months.

On Saturday, Mr. DeSantis avoided Mr. Trump’s legal entanglements or his falsehoods about the 2020 election, instead highlighting the GOP’s recent string of electoral losses. The Republican Party has struggled in every national election since Mr. Trump’s 2016 victory.

“We must reject the culture of losing that has impacted our party in recent years. The time for excuses is over,” Mr. DeSantis said. “If we get distracted, if we focus the election on the past or on other side issues, then I think the Democrats are going to beat us again.”

It’s uncertain whether Mr. DeSantis’ political successes in Florida can be replicated on the national stage.

Even before he formally enters the race, he’s already facing questions about his ability to court donors and woo voters.

The Iowa visit, his second in two months, was expected to help address concerns about his sometimes awkward personal appeal as he met with Republican officials, donors and volunteers, all under the glare of the national media. But Mr. DeSantis devoted little time — at least compared with most of the GOP’s other White House contenders — for selfies or handshakes in Sioux Center, where more than 600 people had gathered to see him at an event billed as a family picnic for Congressman Randy Feenstra.

Mr. DeSantis left most of the politicking to his allied super political action committee, which had set up a table where prospective supporters for his yet-to-be-announced presidential campaign could sign up.

The road outside the museum was flanked with DeSantis 2024 campaign signs.

Mr. Trump’s team had expected more than 5,000 to attend the rally at an outdoor amphitheater in downtown Des Moines for the purpose of collecting information on would-be supporters and encouraging them to commit to Mr. Trump.

Mr. Trump’s 2024 Iowa campaign, unlike his rag-tag 2016 second-place Iowa effort, is putting together a more disciplined, data-driven operation. The Saturday event was aimed at encouraging attendees to sign up with the campaign on a website so the campaign could maintain contact with them, keep them posted on how and where to caucus, and recruit campaign volunteers.

In a social media post, Mr. Trump promised to reschedule the event. Shortly afterward, the campaign released a list of endorsements from more than 150 Iowa elected officials and activists across all of the state’s 99 counties.

And as they compete for support, the emerging rivalry with Mr. DeSantis has turned increasingly personal.

Mr. DeSantis has largely ignored Mr. Trump’s most egregious jabs, which have included suggesting impropriety with young girls as a teacher decades ago, questioning his sexuality and calling him “Ron DeSanctimonious.”

Mr. Trump’s campaign began airing an ad mocking Mr. DeSantis for yoking himself to the former president in 2018 when he ran for governor, even using some Trump catchphrases as a nod to his supporters in Florida.

Mr. Trump’s super PAC, MAGA Inc., also has aired spots highlighting Mr. DeSantis’ votes to cut Social Security and Medicare and raise the retirement age. The group even targeted Mr. DeSantis’ snacking habits, running an ad that called for him to keep his “pudding fingers” off those benefits. That was a reference to a report in The Daily Beast that the governor ate chocolate pudding with his fingers instead of a spoon on a plane several years ago. Mr. DeSantis has said he does not remember doing that.

At the same time, the pro-DeSantis super PAC, Never Back Down, has hired Iowa staff and begun trying to organize support for the governor before a 2024 announcement. The group announced Thursday that state Senate President Amy Sinclair and state House Majority Leader Matt Windschitl would endorse Mr. DeSantis’ candidacy. On Friday, it rolled out roughly three dozen more state lawmakers who would endorse him.

Governor Reynolds and Senator Ernst attended Mr. DeSantis’ Sioux Center appearance.

After his speech, he spent about 15 minutes shaking hands and making small talk with voters as he maneuvered through the large audience, trailed by reporters, TV cameras and a security detail. He then dashed outdoors to pose with Ms. Reynolds and Mr. Feenstra while tending to burgers and pork chops at the grill.

Lyle and Sonia Remmerde of Rock Valley managed a handshake. She said Mr. DeSantis’ style comes across as normal. “One of the things when you compare Trump and DeSantis, I think DeSantis has — how do you say? — a much more smooth approach,” said Lyle Remmerde, 65. “He’s less abrasive.”