Former Florida Gov. Jeb Bush greets supporters following a campaign rally on Thursday in Las Vegas. (Isaac Brekken/AP)

Jeb Bush’s first post-debate political rally started a few minutes early, in a rec center room built for 200 but only half-full. He started with an in-joke, about a candidate who would not be named and whose rallies were at least a basketball stadium larger.

“I hope that I am so brilliant and so eloquent and so high-energy that you feel compelled to caucus for me,” Bush said as chairs were put down to fill out space. After delivering some of his stump speech, he asked if anyone had seen the debate. “It was crazy, different,” he said, before returning to the subjects of 4 percent economic growth, his “heart to serve” and the unaffordable spending plans of Democrats.

Bush did what his aides and supporters said they hoped he would do in Wednesday night’s debate. He showed energy. He demonstrated passion. But the scene in Las Vegas illustrated the challenges facing the former Florida governor, who finds himself in a race unlike anything he expected — or that he’s ever experienced.

Until this summer’s rise of Donald Trump and Ben Carson, Bush had been known for two purple-state gubernatorial wins, in 1998 and 2002. His one election defeat, in 1994, was a razor-thin loss to a popular Democratic incumbent. Even then, he triumphed in a primary against more-established but less-connected conservative rivals.

“He is not by nature a combative person who delights in the fight, but he wins,” said Ken Connor, a conservative attorney who challenged Bush in 1994, then worked with him in the fight to keep Terri Schiavo, who doctors said was in an irreversible persistent vegetative state, on life support. “After he was in office for a while, I told him, ‘Boy, if I knew you were gonna govern this conservatively, I could have saved my time and money.’ ”

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Now, mired in single digits in the polls, Bush is struggling to adjust to an unfamiliar role as an underdog.

Even his debate performance, while more forceful than a previous one, was uneven. At times, his discomfort was clear.

He interrupted front-runner Donald Trump, but moments later, when the billionaire developer and Wisconsin Gov. Scott Walker sparred, Bush stood between them watching the back-and-forth with an awkward grimace. Later, Bush sought to score points by demanding that Trump apologize to his wife for ridiculing her Mexican heritage, but Trump refused to comply and insisted he owed an apology to no one. In the end it was another non-politician, Carly Fiorina, who seemed to have benefited most from the night.

“This is a much bigger field, and we know that most on that stage are superior than what he’s faced before,” said J.M. “Mac” Stipanovich, who managed Bush’s unsuccessful 1994 gubernatorial campaign.

The urgency for Bush and his team to show a change was evident immediately after the debate. Aides emerged from the event exhausted — and determined to aggressively erase doubts about Bush’s vitality and portray any suggestion of his struggles as media hype.

Sweat dripping down his face, campaign manager Danny Diaz entered the post-debate “spin room” and said: “I knew he was going to do a great job. I just need the media to give a fair characterization of it.”

Aides cited two key moments: the apology exchange with Trump, and when Bush responded to Trump’s criticism of George W. Bush by saying, “He kept us safe.”

The second debate for top Republican presidential candidates included bashing Donald Trump, a fiery Carly Fiorina and an admission from Jeb Bush that he says his mom won't like. (CNN)

“He put Trump on his heels and silenced him for 40 minutes — something that nobody’s been able to do,” said Trent Wiseup, a longtime aide who helped Bush prepare for the debate.

An e-mail sent to thousands of grass-roots supporters Thursday warned them: “We’re fighting against the spin artists. Unless we can show that our supporters are behind him, all of this momentum will be lost.”

Top finance aides hosted a 15-minute conference call with donors in hopes of encouraging top bundlers to collect more cash before the fundraising quarter ends on Sept. 30, according to a participant in the call. An e-mail sent Thursday morning to New York-area supporters invited them to a breakfast fundraiser on Oct. 15 and asked attendees to give the maximum $2,700 to the campaign.

One top bundler, requesting anonymity to speak frankly about internal discussions, said the campaign was “trying to convince the entire world that he won the debate. All of it is obviously over the top.” The donor conceded that among some financial backers, “The level of nervousness is rising, more so because of the drop in the polls. There’s sole hope that Wednesday changed things.

The Las Vegas rally demonstrated how far Bush still has to go. Several attendees, when asked about the debate, talked not about Bush’s performance but about Fiorina’s brutally effective comebacks against Trump. But all were at least satisfied by Bush’s new energy.

Vic Sotelo, who once worked on George H.W. Bush’s security detail, arrived early at the rec center with his wife, Pat. Both were happy to hear the candidate defend his family. Both also understood why their fellow Republicans were rebelling.

“People are excited about Trump and Carson and Carly because they don’t have that politician filter,” said Pat Sotelo. “But you need that filter if you want to govern. Jeb’s always polite. A lot of people take that politeness for weakness. I don’t.”

“All those issues that Trump is talking about are serious issues that everyone is thinking about,” said Vic Sotelo. “I think if Jeb addresses those Trump issues with the politeness and the charisma that he already has, he’ll do even better.”

Bush spent less time talking from the rec center’s stage than he spent signing autographs, posing for photos and chatting with potential voters. As he headed for the exit, he took only a few questions, about where he’d go next and why more people didn’t show up for the rally.

“Three o’clock in the afternoon,” mused Bush.

Virgilene Welch, a die-hard Bush fan, left the rally through another exit, clutching bumper stickers and signs with fresh autographs. She was ready to caucus, but well aware that Bush was now an underdog.

“He looks it,” she said. “You saw that at the debate. He wasn’t taking his eyes off the guy he’s gotta beat.”

O’Keefe reported from Los Angeles. Jose A. Del Real and Thomas LeGro in Washington contributed to this report.