Donald J. Trump holds a commanding lead over his nearest rivals for the Republican presidential nomination. One or two might make a dent in the numbers at the first debate this week. But the rest of the field, featuring little-known candidates, is unlikely to make an impact.

In fact, there is almost no plausible path for them to the nomination, especially in a race with Mr. Trump as the dominant force, which raises the key question: Why do they do it?

Perhaps the biggest reason is the debate stage itself: National broadcasts have the potential to provide a biotech entrepreneur, a Miami mayor and a North Dakota governor the chance to become household names and position themselves for future success in politics — or whatever field they pursue.

The longer-than-long-shot candidates — some have run in almost every cycle since cable news and social media became significant drivers in elections — are willing to endure the grueling schedule, the deep loss of privacy and the frequent humiliations of a campaign because there are so many consolation prizes.

Candidates can raise their profiles and polish their résumés for a future bid for office. They can land lucrative commentator gigs on any number of platforms. A presidential run can lead to a high-paying job in the private sector or, of course, a big role in someone else’s administration.

“There are always people who want to make a name for themselves,” said Curtis Loftis, who as the elected treasurer of South Carolina since 2010 has seen a parade of presidential aspirants roll through his early nominating state.

“Some people have personal ambitions that allows them, or requires them, to run for higher office,” he said. “Politics is an industry. People have to keep their name fresh. By losing, they end up on highly paid corporate boards. It’s an industry — it’s not pretty.”

But this campaign, especially, highlights the mixed motives of presidential hopefuls because there is such a large field, even though Mr. Trump overshadows the race like the de facto incumbent.

The trend is somewhat new. Though newcomers have always pursued unlikely campaigns, they were mostly relegated to the sidelines. Even those whose candidacies were largely aspirational relied on their experience in elected office as a reason for running.

The 2012 election was perhaps the tipping point, when Herman Cain, a successful chief executive of a pizza chain, at one point led the Republican primary polls. In 2016, Mr. Trump entered the race in what was seen as a vanity campaign.

The open field for Democrats in 2020 brought plenty of elected experience, but it also garnered attention for outsiders like Andrew Yang, another entrepreneur, and Marianne Williamson, a self-help author, who is running again in 2024. Both participated in the Democratic primary debates.

Strategists of both parties who have worked for candidates with slim chances said it was unheard-of for them to admit privately that their goals were less than the winning the biggest prize. Yet, their behavior often betrays them, including on a debate stage when they decline to take on the front-runner, or, in the case of many of Mr. Trump’s rivals, even to say his name.

“A lot of candidates approach campaigns with an ‘opportunity maximizing’ approach — if you don’t get to the moon, you can at least land among the stars,” said Sarah Isgur, who was a top aide to the long-shot Republican candidate Carly Fiorina in 2016. “They want to make sure not to shut any doors along the way — cabinet, TV contracts, whatever. That’s why you see some of these types of candidates pull so many punches on the stump or debate stage, because they don’t know who they’ll need as friends later on.”

Like defense lawyers who never ask if a client is guilty, paid strategists mount the best campaign possible given a candidate’s skills, message and budget.

Still, strategists’ gut instincts usually tell them how their clients have inwardly set their sights. “You can tell right away if they’re really running to lead or if they have other goals in mind,” said Gail Gitcho, a strategist who has worked for several Republican presidential candidates, including Vivek Ramaswamy, the conservative commentator, before she parted ways with him this spring.

“Some candidates are running for president, others are running to replace Tucker Carlson,” Ms. Gitcho said.

It goes without saying that getting candidates in the heat of campaign battle to admit to ulterior motives is a fruitless quest. Invariably, they cite outsiders like Jimmy Carter, Barack Obama and Mr. Trump himself who went all the way.

But the rise of the wealthy, self-funded candidates brings in a whole new factor to a campaign. Perry Johnson, a Michigan businessman hovering around one percent in polls despite crisscrossing Iowa, said that raising his profile to increase his net worth was the furthest thing from his mind.

“I am a very rich man, I don’t need any extra money,” Mr. Johnson said in an interview in Cedar Rapids, Iowa. “I expect to win this presidency. I am the one guy that the country truly needs.” He is one of a handful of multimillionaires seeking the nomination. (Egos, too, are rarely in short supply for the long shots running for president.)

Even the longest of long shots — candidates with no electoral experience and limited political charisma — believe they might catch lightning in a bottle.

And if not, perhaps they can capture the attention of the front-runner. Voters who attend events in Iowa or New Hampshire with Mr. Trump’s rivals openly say they are looking to see who could be a running mate — maybe Senator Tim Scott of South Carolina, or the former U.N. ambassador Nikki Haley, or Mr. Ramaswamy.

A New York Times/Siena College Poll last month showed Mr. Trump with 54 percent of the likely Republican primary vote, Mr. DeSantis with 17 percent and all others at 3 percent or less, including former Vice President Mike Pence, Mr. Scott, Ms. Haley and Mr. Ramaswamy.

Gov. Doug Burgum of North Dakota, little known outside his state until recently, made it into the debate partly by offering $20 gift cards for a $1 donation, helping him clear the threshold of 40,000 individual donors to participate.

“We’re running for president, and we actually think we have an excellent chance,” Mr. Burgum said in an interview, speaking in the first-person plural as if his candidacy was a movement.

He dismissed Mr. Trump’s utter dominance of early polls as a reason not to run.

“You wouldn’t say so-and-so is going to win the Super Bowl next February, we’re just going to cancel the season,” he said. “No, you play the game. America loves competition. America loves an underdog story, too.”