Sen. Marco Rubio (R-Fla.), seen here campaigning in New Hampshire last week, is settling into his role as rising top-tier candidate. (Charles Krupa/AP)

As Marco Rubio settles into his new role as a rising top-tier candidate, most of his opponents in the Republican presidential race are showing a reluctance and even an unwillingness to engage him directly on the national stage.

The spotlight on Rubio is intensifying in the media as journalists investigate the senator’s political record and background. But he otherwise is left facing relatively low hurdles for now, bypassing the kind of heated personal clashes that have shaped the 2016 nomination race.

For Rubio, it is a return to the lofty status he had after he burst onto the national scene five years ago. Many Republican elites are once again celebrating him as the party’s golden boy, if not its strongest general-election candidate, and fear seeing him bruised too badly during the primary season.

“He’s articulate, attractive and young. His rivals don’t want him to win, but no one wants to lose him,” said Vin Weber, a prominent Jeb Bush supporter. “Of course, politics is a rough-and-tumble sport, and he’ll need to take a few punches. But at the end of the day, this is a party that needs to find ways to appeal to Hispanic voters, and having him on our side is an asset.”

The other candidates have not figured out how to deal with what some are calling “the Marco moment,” hinting at critiques and possible anti-Rubio ads to come but hesitating to make Rubio their main target.

Donald Trump has castigated Rubio on the stump and in Twitter messages as a “total lightweight” who is “weak” on immigration. But under the prime-time glare of Tuesday night’s Republican presidential debate, the outspoken mogul fell silent about the senator from Florida.

When Sen. Ted Cruz (Tex.) tried to draw a contrast, he did so only with a thickly veiled line about sugar subsidies, something few voters could connect to Rubio.

And although Bush’s campaign previewed a litany of possible attacks on Rubio, the former Florida governor didn’t say a word in Milwaukee about his onetime protege.

Bush sees Rubio as a direct competitor for the support of wealthy donors and party leaders. Bush’s campaign and its allied super PAC, Right to Rise, have signaled possible lines of attack: In a strategy presentation to donors a couple of weeks ago, the Bush campaign branded Rubio disparagingly as a “GOP Obama.”

In the candidates’ Oct. 28 debate, Bush lunged at Rubio over his spotty Senate voting record, even suggesting that he resign his seat. But the offensive backfired, and in the two weeks since, Bush has steered away from Rubio. The dilemma is further complicated by pressure from many of Bush’s Florida-based financial backers, who also like Rubio and want Bush to go easy on him.

Asked why Bush did not scrutinize Rubio during the Milwaukee exchange, campaign manager Danny Diaz said the debate “was a serious one where important issues were discussed,” and he urged reporters to stay tuned for the next debate on Dec. 15. “We look forward to catching up with all our good friends in Las Vegas,” Diaz said.

Bush’s surrogates indicated that more heat on Rubio would arrive in short order.

“It’s a long campaign,” Al Cardenas, a Florida-based Bush supporter who also is close to Rubio, told reporters in Milwaukee. “Everybody’s going to be scrutinized. Those who do well will get scrutinized more.”

GOP strategist Ari Fleischer put it more bluntly: “The candidates will chop each other up if they thought it would help them. Every one of those candidates think it should be them, and they can give you every reason why it shouldn’t be Rubio.”

The mostly substantive nature of Tuesday’s debate, sponsored by Fox Business Network and the Wall Street Journal, did not invite many personal skirmishes. In one exception, Rand Paul went after Rubio for wanting to increase military spending. But in a tense exchange with the senator from Kentucky, Rubio responded by articulating a hawkish worldview and portrayed Paul as championing an “isolationist” foreign policy.

Trump described the debate’s atmosphere as lacking fireworks. “It was amazing, because the lights went on and you never know what’s going to happen — are you going to be attacked and do you go for the kill, right?” he said Wednesday on MSNBC’s “Morning Joe.” “That was not really necessary.”

Trump’s campaign manager, Corey Lewandowski, said the billionaire contender will continue to talk about his differences with Rubio, especially on immigration.

“People are going to keep looking at Rubio’s record,” Lewandowski said. “They’re going to ask themselves if they really want another first-term senator as president, someone who may not have the right experience. Those concerns aren’t going away.”

Rubio’s advisers presented the lack of engagement Tuesday night as a sign of Rubio’s strength.

“The phrase where I come from is ‘There’s no education in the second kick of the mule,’ ” Terry Sullivan, Rubio’s campaign manager, told reporters. “I kind of feel like folks figured out that taking on Marco isn’t such a great idea. . . . I don’t think anybody’s really itching to take on Marco on the debate stage.”

Perhaps the best encapsulation of Rubio’s good fortune came when moderator Maria Bartiromo asked him how his résumé stacks up against Democrat Hillary Rodham Clinton’s decades of service. Rubio could not help but grin. It was the softest of softballs — an opening for the 44-year-old senator to cast himself as the candidate of the future.

Eric Fehrnstrom, who was an adviser to 2012 GOP nominee Mitt Romney, said Rubio “has a gift of the golden tongue.”

But he added: “I don’t think any candidate on that stage thinks that they’re somehow immune from political attacks. Rubio’s biggest vulnerability is immigration. While he did not address that at length [in Tuesday’s debate], I would expect when the attacks go up on TV that immigration will be in the mix.”

Supporters of rival campaigns voiced surprise that Rubio was not drawn into the immigration discussion, considering his leadership in 2013 on the Senate’s “Gang of Eight” pushing for comprehensive immigration reform. Rubio has since disavowed the legislation and has hardened his immigration positions overall.

“There should be more scrutiny of Rubio, no doubt about it,” said Bob Smith, a former senator from New Hampshire who is backing Cruz. “It’s almost as if the media is ignoring his immigration record, or at least not giving it much coverage. Conservatives up here, however, are well aware of it, and my sense is that they’ll continue to vet Rubio on their own.”

Dan Pfeiffer, a former senior adviser to President Obama, said other Republican candidates may be afraid of tangling with Rubio in a debate.

“Rubio is skilled at delivering a scripted, rehearsed counterpunch, and they had to know he would be prepared,” Pfeiffer said. He added that Cruz seems to be “patiently waiting for his moment to make this attack. Cruz wants to see the whites of Rubio’s eyes before he fires his biggest guns.”

Indeed, Cruz has been laying the foundation for the contrast he hopes to make with Rubio if the nominating contest narrows to the two of them, as some pundits predict. In debate after debate, Cruz has positioned himself as a hard-line opponent of amnesty, and more generally as a conservative purist.

In his immigration comments Tuesday night, Cruz did not single out Rubio. But his advisers did with reporters afterward.

The freshman Texan “will draw contrasts on issues,” Cruz spokesman Rick Tyler said. “Senator Rubio was for the Gang of Eight. Senator Cruz wasn’t. Right now, we’re just beginning that, and we’ve got three months till Iowa.”

Jose A. DelReal in Washington contributed to this report.