Republican presidential candidates fought over immigration reform, health care and peace in the Middle East during the CNN/Telemundo debate in Houston on Feb. 25. (Sarah Parnass/The Washington Post)

A feistier Sen. Marco Rubio of Florida emerged on the debate stage here Thursday night, taking the fight for the GOP nomination directly to front-runner Donald Trump and attacking him as a hypocrite on the immigration issue that has fueled Trump’s remarkable political rise.

Sparring between the two dominated the debate, turning the other three candidates on the stage into bystanders for much of the evening.

Rubio’s aggressive and bold move came at an urgent moment in the Republican presidential race. Trump has won three state contests in a row, building momentum that could make him unstoppable as the campaign moves from a series of single-state skirmishes to a national battlefield in next week’s Super Tuesday contests.

Many consider Rubio the Republican establishment’s best — and possibly last — hope to prevent Trump from becoming the party’s standard-bearer.

His robust performance stood in contrast to his robotic, scripted demeanor at an earlier debate in New Hampshire, which Rubio himself has blamed for his poor showing there. Rubio has also been accumulating what could be a critical mass of endorsements and support from Republican donors and elected officials.

Rubio mocked Trump’s often-repeated claim that he is responsible for elevating the immigration issue and putting it onto the front line of the campaign. The Florida senator accused the billionaire real estate developer of hiring foreign labor over Americans, noting that Trump was sued and fined for underpaying undocumented Polish workers when he was building his Trump Tower in the 1980s.

“You’re only person on this stage that has ever been fined for hiring people to work on your projects illegally,” Rubio said.

“I’m the only one on the stage that’s hired people. You haven’t hired anybody,” Trump retorted. “You haven’t hired one person, you liar.”

At some points, Sen. Ted Cruz of Texas, who is also seeking to ascend as Trump’s primary foe, joined Rubio in a sort of tag team. Cruz noted that he had battled a 2013 effort supported by Rubio to pass immigration reform and give illegal immigrants a pathway to citizenship.

“Where was Donald? He was firing Dennis Rodman on ‘Celebrity Apprentice,’ ” Cruz said, mocking Trump’s long career in reality television. He then said Trump had donated to many of the reform bill’s sponsors: “When you’re funding open-border politicians, you shouldn’t be surprised when they fight for open borders.”

Casting Trump as insufficiently conservative, Cruz said the last person that those on the right should want in the White House is a businessman who is legendary for dealmaking.

Tracking the race to the Republican nomination

“He is promising if he’s elected he will go and cut deals in Washington. And he’s right. He has supported — he has given hundreds of thousands of dollars to Democrats. Anyone who really cared about illegal immigration wouldn’t be hiring illegal immigrants,” Cruz said.

Trump lashed out at Cruz, noting his reputation as the least-liked member of the U.S. Senate.

“You get along with nobody,” Trump said to Cruz. “You don’t have the endorsement of one Republican senator and you work with these people. You should be ashamed of yourself.”

As the two senators persisted with their barbs, Trump resorted to name-calling. “This guy is a choke artist, and this guy is a liar,” he said of Rubio and Cruz, respectively. At another point, he called Cruz a “basket case.”

The debate — held at the University of Houston and sponsored by CNN, Telemundo and Salem Radio Network — was the 10th for the Republicans this election cycle. It was also the first since former Florida governor Jeb Bush, who early on had been considered the presumptive front-runner, bowed out of the contest.

That left only five contenders on the stage for the final faceoff before 11 state contests next Tuesday. A total of 595 delegates — nearly half the total needed to get the nomination — will be up for grabs.

The Super Tuesday balloting will also mark the moment at which the presidential campaign goes national. While many of the states that will be voting are in the deep-red South, the contests will stretch across the map.

Texas, with 155 delegates, is the biggest prize of all. A win here is most critical for Cruz, who has been leading in most public polls and who will find it difficult to go forward if he is defeated in his home state.

Trump taunted him by citing one recent poll: “I’m tied in Texas, which I shouldn’t be.”

When Cruz replied that polls also show Trump losing to likely Democratic nominee Hillary Clinton, Trump fired back: “If I can’t beat her, you’re really going to get killed.”

“Keep fighting. Keep swinging for the fences,” Trump added, dismissively.

Cruz, who campaigns as a moralistic and ideologically pure conservative with the slogan “TrusTed,” has been under intense attack from rivals over allegations that his campaign has engaged in dirty tricks and smears of other candidates.

As a result, the bombastic senator from Texas has found himself in the unfamiliar position of having to play defense; he recently fired a top aide who had posted a video that inaccurately portrayed Rubio as disparaging the Bible.

The prospect of Trump emerging as the GOP nominee, once seen as almost unthinkable, is now starting to look nearly inevitable — especially if all the other candidates stay in the race and continue to split the anti-Trump vote.

What’s left of the party establishment, which nearly always got its way in the past, seems impotent against the celebrity billionaire. Gone is their confidence that his poll numbers were a bubble and that he would be the architect of his own undoing.

Trump has shattered all the conventions of Republican politics and been rewarded for it with victories in the last three states. His most recent was on Tuesday in Nevada’s caucuses, where he left Rubio and Cruz in the dust more than 20 percentage points behind him.

Both Rubio and Cruz have been spinning the outcomes of the first four primaries and caucuses into the illusion of momentum for themselves. Rubio touts as victories his second-place finishes in South Carolina and Nevada; Cruz has been harking back to his Iowa win, noting that he is the only GOP candidate who can claim a notch against Trump.

Another candidate on stage, Ohio Gov. John Kasich, had a surprising second-place finish in New Hampshire, but it has not paid dividends in the subsequent states. He is hoping for future successes in the industrial Midwest, and particularly his home state of Ohio on March 15, to gain traction.

Kasich repeatedly took a different tack from his competitors, suggesting pragmatism and bipartisanship as means to solving immigration issues and saying deportation was not feasible.

“I don’t think we’re going to ride around in people’s neighborhoods and grab people out of their homes,” Kasich said, praising the centrist politics of former president George H.W. Bush, who was in the audience.

Meanwhile, long-shot candidate and retired neurosurgeon Ben Carson, despite early promise, has not found an opening anywhere. But talking to reporters before the debate, he insisted that he is in the race to stay.

On the stage with the other candidates, Carson offered himself as someone who could attract new people to the political process and redefine the Republican Party to voters who have fallen away. “We are compassionate,” he insisted about his own party.

Trump also took fire over his reluctance for now to release his tax returns. A day earlier, 2012 Republican nominee Mitt Romney made headlines by speculating that a “bombshell” may lurk in those documents.

Trump defended his position by stating that he is currently undergoing an audit. “You don’t learn anything from a tax return,” Trump said, but said he would eventually release them.

“As far as my return, I want to file it,” Trump said. “I will absolutely give my return but I’m being audited now.”

“The voters need to know,” Cruz said.

Trump knocked conservative radio host Hugh Hewitt, who asked about the returns. “Very few people listen to your radio show,” he told him.

On foreign policy, there were fireworks over Trump’s recent comment that he would be “neutral” on the Israeli-Palestinian conflict.

“The next president needs to be someone like me who stands firmly on the side of Israel,” Rubio said. “They are the only pro-American, free-enterprise democracy in the Middle East.”

The weeks that follow Super Tuesday may bring a dramatic change in the pace of the battle for the nomination. Until March 15, delegates will be awarded proportionally, in most cases by congressional districts. That means that all of the candidates are likely to come away with their delegates totals boosted, even if they do not win any states outright.

After that, most of the primaries will be winner-take-all. If one candidate prevails in all or most of them, he will go hurtling toward the finish line.

David A. Fahrenthold contributed to this report.