MIAMI — From one of the earliest moments of the debate, former congressman Beto O’Rourke demonstrated the promise and the peril of his presidential candidacy.

He spoke of bringing the country together, and he surprised some of his competitors by breaking into Spanish and displaying a fluency with connecting with Latino voters. But underneath it all he failed to answer a basic question on what has emerged as a big issue in the primary campaign: whether he would support a 70 percent tax rate on the wealthy. He then dodged a follow-up question, and then another.

Time and again, O’Rourke’s answers seemed to fall flat, and so did much of his night.

The magnetic candidate who sprang from a nearly successful Senate bid in Texas has been unable to fully translate the appeal of his 2018 campaign to the mood of the national party ahead of 2020, with Democrats appearing hungry for a clear agenda and for someone who can exude strength against President Trump.

Wednesday night’s debate, the first of two nationally televised encounters involving 20 contenders for the Democratic nomination, showcased the deep divisions playing out inside the party on major issues such as economics, health care and immigration — with the candidates ahead in the polls representing dueling visions for the future. Much of the policy discussion was shaped by the liberal ideas of Sen. Elizabeth Warren (D-Mass.), while Thursday night’s conversation was expected to be dominated by the clashing views of former vice president Joe Biden and Sen. Bernie Sanders (I-Vt.).

But O’Rourke, who energized many party activists last year during his Senate campaign and offered the promise of a new generation of national leadership, repeatedly struggled onstage to articulate some of his more moderate views.

He was frequently attacked by his rivals in a way that could have offered him a chance to strongly defend his positions on immigration and health care. But he seemed ill at ease and unprepared to face any pointed criticism. And if candidates who have been polling below him and raising a fraction of the money he has can rattle him in a debate — as it seemed fellow Texan Julián Castro did during one notable exchange — some began openly wondering: What would Trump do to him?

“The problem for him is not just that it was a bad night — it’s that he needed a really good night to reignite his candidacy. He squandered the opportunity,” said David Axelrod, a longtime Democratic strategist who has been drawn to O’Rourke’s brand of hopeful politics. “I say this as someone — I like him. But I think even his folks have to recognize it was not a good night.”

“Whenever his more moderate positions come up, he’s just not that good defending it,” he added. “He just did not look strong. And strength is sort of a prerequisite for this job.”

O’Rourke on Thursday sought to defend his performance, chalking it up to a debating style in which he doesn’t try to contrast himself with others in the race.

“I choose to define myself not against other people. I’m really running not against any of those other candidates but for the United States of America,” he told CNN. “Others had a different strategy, one that involved attacking other candidates, and I’ll leave it to pundits and others to judge performance or the best tactics that one could take.”

O’Rourke’s candidacy, with a rapid rise and a swift stall, has been one of the looming questions of the early part of the 2020 primary campaign. He launched with gushing praise from Oprah Winfrey, a Vanity Fair cover story and a crush of media attention during his first trip to Iowa. His campaign began building a grass-roots network and raised record sums in the first 24 hours after he announced.

But he has struggled to maintain a strong presence as voters have demanded more substantive answers and as the dynamics of the race have shifted. South Bend, Ind., Mayor Pete Buttigieg gained new interest from those searching for a generational candidate. Biden has taken a commanding spot for those looking for a pragmatic centrist.

The debate Wednesday put O’Rourke again in a new space, on national television, with tight time limits and combative peers, far from the intimate town halls where he built his political career. O’Rourke has been learning to adapt ever since he launched his campaign, engaging more with television interviews and quick message delivery.

“He likes being with and around people. That’s why he has hosted town halls and visited so many communities,” said Steve Ortega, a longtime friend of O’Rourke’s who served with him on the city council in El Paso. “Even when he was in Congress he was not the first to go on all the cable news shows,” Ortega continued. “With people one-on-one, I have never seen anyone better.”

After the debate, Ortega texted O’Rourke to congratulate him, telling him he did well. “Thanks,” was the reply.

O’Rourke’s advisers were adamant that they were pleased with the debate and all of his answers. Just because he didn’t bicker with his rivals or criticize their plans, they argued, did not mean that he wasn’t able to put forward his own vision. They touted his willingness to speak Spanish — and not just on issues related to immigration — and said they had gotten good feedback from watch parties they held.

“We had no concerns about last night’s debate,” said Chris Evans, the campaign’s communications director. “Quite the opposite — we are excited about what he did to introduce himself to voters and how he connected.”

O’Rourke spoke for just over 10 minutes during the debate, earning more time than every other candidate aside from Sen. Cory Booker (D-N.J.). But when his positions were scrutinized, he seemed unsteady and allowed other candidates to take control.

In the second question directed to O’Rourke, NBC’s Lester Holt asked him to explain his shift from supporting Medicare-for-all to backing a public option that retained private health insurance. His answer, which involved a man he met in Laredo with glaucoma, described his current plan to allow choice and get expanded care quickly but did not explain his shift.

He was immediately attacked by New York Mayor Bill de Blasio: “Why are you defending private insurance to begin with?”

O’Rourke was not able to respond, because former Maryland congressman John Delaney interrupted to defend his own health plan.

“I think we should be the party that keeps what’s working and fixes what’s broken,” Delaney said, triggering applause.

That set the tone for much of the night, with O’Rourke attempting to deliver personal stories, as he would at a town hall, only to find himself interrupted or challenged — and failing to address the question before him.

When O’Rourke was asked by moderators about how he would handle unauthorized immigration, Castro interrupted to attack, challenging O’Rourke to explain why he did not support a plan to repeal the criminal penalty for crossing the border without permission. O’Rourke said he was looking for a broader solution, without addressing Castro’s question directly.

The exchange allowed Castro to direct several zingers at O’Rourke — who lives on the U.S.-Mexico border and who has sought to make immigration a core issue of his campaign. He did not respond in kind.

“I think you should do your homework on this issue,” Castro said at one point.

O’Rourke did a round of interviews Thursday morning, saying that he felt he was under frequent attack during the debate.

“I’d give myself an A. I wanted to make sure that I got that point across — I described why I’m doing this, who I’m doing it for, the people that inspire me and how we’re going to meet these challenges,” he said on CNN. “And it felt like I was able to get that across.”

Later Thursday, he went to a children’s migrant shelter in Homestead, Fla., to denounce the Trump administration’s treatment of immigrants. O’Rourke was the first presidential candidate to announce that he would visit the shelter, which helped trigger a large number of other candidates to plan visits as well, with several making stops there Wednesday before the debate.