Lying in an Afghan desert, engulfed in flames and soaked in diesel fuel, Sam Brown realized he was about to die.

It was September 2008, and Mr. Brown, who was a U.S. Army lieutenant at the time, had been leading his platoon to the aid of fellow soldiers who had been ambushed by the Taliban. Then, his Humvee struck a roadside bomb. In an explosion of fire and concussive sound, Mr. Brown’s life was forever changed.

“I remember laying there, facedown in the dirt in the Kandahar desert, trying to scoop dirt over myself to smother the flames and having no success, and thinking to myself: How long will it take to burn to death? What happens as I die?” Mr. Brown recalled in an interview with The New York Times. “And then literally making the decision to give up the will to live.”

But he survived. A fellow soldier, also injured in the blast, saved Mr. Brown, and his platoon provided first aid until he could be evacuated to a hospital. At a burn unit in Texas, he underwent more than 30 surgeries over a three-year recovery, and he was left permanently scarred.

Now, Mr. Brown, 40, who medically retired as a captain, is the leading Republican seeking to challenge Senator Jacky Rosen, a Democrat, in what is expected to be one of the most competitive Senate races this cycle, with the potential to determine control of the chamber. At campaign stops, Mr. Brown does not dwell on his dramatic history, focusing instead on inflation, which many Nevadans have felt acutely, and on the border. But his experience is a central part of his appeals to supporters as he works to raise the kind of money needed to run a statewide campaign against a well-funded incumbent.

His emails frequently contain lines like “God is real. I almost met Him” and “They blew up my body, but they’ll never destroy my spirit.” He has compared headlines about President Biden’s “fiery” demeanor with his own burn scars. “You want to see fiery, Friend? I’m literally fiery,” read one email, which included a photo of his scarred face. “I will stand in the fire. I will take the flames.”

And Mr. Brown was inspired to run for office, he said, because he wanted to help people suffering through their lowest moments, the same way that a comrade had saved him in Afghanistan.

“I see a lot of hopelessness in our country right now,” he said, “and I’m coming into this Senate race with a perspective of, I’ve been the recipient and a blessing of someone coming to my aid when I needed it most.”

Mr. Brown, who fell short in the 2022 Republican primary for Senate in Nevada and has never held elected office, could face a formidable opponent in Ms. Rosen. Her campaign plans to emphasize her bipartisan reputation while arguing that Mr. Brown’s relatively short time in the state — he moved from Dallas to Reno in 2018 — and the various start-up, nonprofit and consulting jobs he has held over the past 12 years, since leaving the military, do not make him best suited to help Nevadans.

Democrats are particularly eager to highlight Mr. Brown’s past opposition to abortion, and his recent attempts to soften his stance. (A measure enshrining abortion access in the state’s Constitution is expected to be on the ballot in November, and Democrats nationally have been energized in recent elections by the political potency of the issue.)

Still, Mr. Brown may be sidestepping some of the pitfalls of other recent nominees who were perceived as too extreme for the general Nevada electorate by avoiding a bruising primary fight, said Amy Tarkanian, the former chairwoman of Nevada’s Republican Party.

With a big financial and polling edge — surveys show him up double-digits in the primary on June 11 — Mr. Brown skipped a debate with his rivals. Though he has attended some community events, he has not been especially ubiquitous on the campaign trail. In February, he acknowledged to guests at a Nevada Republican Club lunch in Las Vegas that he has held relatively few campaign events in the state as he traverses the country raising money. (His campaign, which raised $2.4 million in the last quarter, has set a goal of raising $20 million overall.)

What Mr. Brown has done is work to appeal to independents who could sway the general election, rather than solely to conservative voters, in part by shifting his rhetoric on abortion. He has also avoided tying himself too closely to former President Donald J. Trump, though he has been more vocal about his praise for Mr. Trump in recent months.

“I find it refreshing when you have a Republican who’s willing to dig their heels in and say, ‘No, this is what I believe. I’m not going to cave to the far-right noise,’” Ms. Tarkanian said.

His primary rivals — and Ms. Rosen’s campaign — have been less impressed. Mr. Brown waited to endorse Mr. Trump until January, a delay that did not go unnoticed on the right.

“He barely even says President Trump’s name,” said Jeff Gunter, a primary candidate who was the ambassador to Iceland under Mr. Trump. “That’s part of the scam — making voters think he’s somehow supportive of the president, and he’s really, really not.”

Mr. Brown has recently been more outspoken about his support for Mr. Trump and his own conservative bona fides, appearing on television networks like OAN and Newsmax, and on the podcast of Wayne Allyn Root, a right-wing conspiracy theorist. “President Trump’s policies very clearly, in my view, had Americans in a much better spot than they are today,” Mr. Brown said. At a campaign event in Reno on Saturday, he told reporters that he was “extremely conservative.”

Mr. Trump has not made an endorsement in the race, but he has shared several images on his social media site, Truth Social, that seem to indicate his enthusiasm for Mr. Brown. “Democrats are terrified of a united Trump-Brown ticket in Nevada!” one post read. (Nevada’s governor, Joe Lombardo, a Republican, has endorsed Mr. Brown.)

On abortion, Democrats say that no amount of moderating language will convince voters that his views have truly changed.

“Sam Brown’s record shows he is pushing an extreme MAGA agenda that would hurt hardworking Nevadans,” said Johanna Warshaw, a spokeswoman for Ms. Rosen’s campaign.

During a run for the Texas Legislature in 2014, while living in Dallas, Mr. Brown endorsed a 20-week abortion ban with no exceptions for rape or incest, and in the past he has declined to say whether he would support a national ban on the procedure. After his first Senate run, he served briefly as the chairman of Nevada’s chapter of the Faith and Freedom Coalition, a conservative Christian group that is vocally opposed to abortion.

More recently, he has sought to clarify his stance. In an interview with NBC News in February, his wife, Amy Brown, recounted her own difficult and emotional decision to get an abortion when she was 24 and amid an unplanned pregnancy. In that interview, Mr. Brown said he would not support a national ban, agreed with Nevada’s current law allowing abortions until 24 weeks of pregnancy and supported exceptions for rape, incest and the life of the mother.

In the interview with The Times, he reiterated that position, while saying that he believed abortion should be left to the states — a stance Mr. Trump has also embraced.

“I cannot do anything to change Nevada’s laws, nor do I seek to change Nevada’s laws,” Mr. Brown said, adding, “I would not support a federal abortion ban.”

Some Republicans suggested that Mr. Brown still needs to ensure that voters know his position on this and other issues — not just his life story.

“As people are meeting with him or listening to him present at meetings, they’re finding that there needs to be more than just the military story,” Ms. Tarkanian said. “And he’s been in Nevada long enough now just to run in a second election, whereas Jacky Rosen has been in Nevada for, I think, over 40 years.”

Mr. Brown’s campaign argued that he had detailed his stance on a variety of issues — including those as esoteric as cryptocurrency — and has substantive experience beyond his military background, pointing to his business degree and his time running a pharmacy benefit manager, a company that helped veterans get their medications.

The campaign hopes to make the race a referendum on Ms. Rosen, arguing that she has done little to help Nevadans struggling with high gas prices and housing costs.

Still, his success may ultimately hinge on whether his personal story resonates with voters. Mr. Brown “has the ability to drive one message that every voter will know come Election Day,” said Jeremy Hughes, a Nevada Republican political strategist. “Whether voters’ singular understanding of the sacrifice of Sam Brown’s military service is enough to win him the race will be the open question.”