DALLAS-Vice President JD Vance looked very much like a presidential candidate-in-waiting at the Republican convention this week. He delivered a prime-time address, met with delegates from battleground states and headlined a high-dollar fundraiser with GOP donors.

Vance's Thursday night speech fired up the crowd, as he laid out his vision for the America he wants his children to grow up in, while painting Democrats as extreme. During the speech, audience members said the quiet part out loud, shouting "48!" Donald Trump is the 47th U.S. president, and the next one will be the 48th.

The moment is likely to solidify Vance's rising status as the Republican front-runner heading into the 2028 election. "I think the country is really getting to know him," said Michael Foster, 32 years old, of Raleigh, N.C. "I'd be shocked if he hadn't sealed the deal tonight."

Yet over the duration of the two-day convention, another name also surfaced: Marco Rubio. The secretary of state was more than 3,000 miles away, wrapping up a diplomatic tour of South America.

In more than three dozen interviews on the sidelines of the convention, many people mentioned Vance and Rubio in the same breath, openly debating which man should be at the top of the ticket in 2028. Some said they should run together. Others held out hope that Trump would defy the Constitution and run for a third term, or that he would campaign as Vance's vice president.

Convention attendees rarely mentioned other potential GOP presidential candidates.

"Oh, we love JD. He's just so forthright and he's so humble, I just think he's going to make the best president," said Gayle Hepler, a 69-year-old mortgage broker from Vancouver, Wash.

"Man, it's hard," said Ron Petri, a minister from Dallas. "It's Rubio, but then I'll be like, I can see Vance. I think it's going to be Vance. He's closer to the youth movement."

The Vance-or-Rubio debate-which unfolded in private conversations on the sidelines of the convention, and in nearby restaurants and hotel bars-reflected broader uncertainty among donors, conservative activists and the president himself over who should lead the post-Trump Republican Party.

"I'd love to see him do like a TV show, like 'The Apprentice,' and have them all in there and at the end endorse one," said North Carolina Rep. Richard Hudson, chair of the House Republicans' campaign arm, referring to the reality show that Trump once hosted.

Trump has at times appeared to pit Vance and Rubio against each other, polling friends and associates about whom they prefer. He isn't doing that as much these days, according to aides and others close to him. He was impressed with Vance's media appearances during a book tour this summer, including a stop on "The View," the aides said.

Lately, Trump has become fixated on another idea: How to get the two men on the same ticket, considering it unbeatable, according to people familiar with his thinking. Such a move is unlikely, despite Vance and Rubio's close friendship, allies of both men said, because neither would want to be vice president.

Many convention attendees similarly held out hope that the vice president and cabinet secretary would be running mates, saying their names as though they were one word: VanceRubio. "I love those two guys," said Sandra Bush, 76, of San Antonio, who was wearing a full-length sequin gown reminiscent of the Texas state flag.

Rubio's absence from the two-day convention in Dallas has sparked speculation about whether he wanted to distance himself-as other Republicans have-from a Trump-designed spectacle at a challenging moment for the party. Rubio has said his role as the nation's top diplomat means he should stay out of domestic politics.

Still, during a three-day swing through South America, Rubio was received with more than a few winks toward his political future. In Barranquilla, when Rubio joked that Colombia's new leader, Abelardo de la Espriella, "went crazy and decided to run for president," his host pointed at the secretary of state and declared to the cameras: "He's next!"

Asked by reporters if he dreamed of becoming president, Rubio quipped, "I don't know what the future holds, but I have no plans at this time." Rubio, 55, said he was focused on his work in the administration, which also includes serving as Trump's national security adviser. He has told associates he wouldn't challenge Vance, 42, if he runs in 2028, The Wall Street Journal previously reported.

A spokesman for Vance declined to comment. Representatives for Rubio didn't respond to a request for comment.

Earlier Thursday, Vance met with delegates from Ohio, Pennsylvania, Michigan and Wisconsin-states that will be crucial in the next presidential election. He also hosted a GOP fundraiser that pulled in $2 million, according to people familiar with the event. Vance has boosted his profile with top donors in his role as finance chairman of the Republican National Committee.

Deb Spencer of Boyd, Texas, said she loves both Vance and Rubio, but she wants Vance to be more visible in the coming months. "We've been seeing Rubio all the time," she said. "We need to see JD more out in public-much more than we are."

Andre Stafford, 25, said he would back Rubio if the Republican presidential primary were held today. "Marco Rubio has been doing a fantastic job as secretary of state, and I am so sad that he's overseas right now and not with us," said Stafford, who is running for a state House seat in Georgia.

"I would love for Trump to run again but I would hate for a Democrat to get into office and do the same thing. So as much as I love the president, I think it's time for him to go hang out at Mar-a-Lago," Stafford said.

Vance, if he decided to run, is unlikely to have the field to himself. With Trump no longer eligible to run, a host of ambitious Republican lawmakers are privately eyeing the race, and there could also be outsider candidates. Sen. Ted Cruz of Texas is openly toying with the idea.

Celeste Cabrera Huff, who is running for a state House seat in Texas, said she has her own theory about who might be the nominee in 2028-and it doesn't involve Vance or Rubio.

"We're hearing Trump 2028, but we're not seeing which Trump," she said, signaling it could be one of Trump's children. "Who knows? We would support it."