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Donald Trump and Sen. Ted Cruz participate in a Republican presidential debate Feb. 25, 2016, in Houston. Michael Ciaglo-Pool/Getty Images

UPDATE: 10:48 p.m. EST -- GOP front-runner Donald Trump was asked why he supports building a wall along the U.S.-Mexico border, but not also along the Canadian border. The moderator said Canada was also considered potentially a significant threat by security officials. He responded that Mexico posed a major problem not just due to people coming in, but also drugs, and that the Canadian border was simply too long.

Trump responded: "It would be very, very hard to do, and I don’t care what anyone says, it is not a big problem," he said, referring to the Canadian border.

UPDATE: 10:33 p.m. EST -- Presidential contenders were pessimistic about a negotiated ceasefire taking hold in Syria. GOP front-runner Donald Trump said it was unlikely to hold because not all parties were part of it, and Texas Sen. Ted Cruz said he was also "skeptical."

Florida Sen. Marco Rubio and Ohio Gov. John Kasich faulted the current violence in Syria, as well as the rise of the Islamic State group, on a U.S. failure to aid rebels early on. "We should have been supporting the rebels long ago," Kasich said.

Trump said the U.S. should have stepped back. “We would be better if the politicians took a day off instead of going into war," he said.

UPDATE: 9:56 p.m. EST -- GOP front-runner Donald Trump was asked how he would cut spending and trim the national debt. He said he would "cut so much your head will spin" and blamed alleged overspending on "waste, fraud and abuse."

Ohio Gov. John Kasich said he has experienced balancing a budget and said it's not just about cutting, but also "innovation" and creating better opportunties. He said he's created hundreds of thousands of jobs in Ohio and has managed to diversify the economy.

"I will go back to Washington and do it again for the American people," he said.

UPDATE: 9:37 p.m. EST -- Asked about the death of Supreme Court Justice Antonin Scalia, candidates said they would nominate conservative judges, and Texas Sen. Ted Cruz was questioned whether GOP front-runner Donald Trump would do the same. Several of the candidates, including Ben Carson, Ohio Gov. John Kasich and Florida Sen. Marco Rubio, emphasized the importance of religious freedom.

Rubio, doubting Trump backed conservative values and would support a conservative judge, said: "Until recently, he was still defending Planned Parenthood."

UPDATE: 9:20 p.m. EST -- All gloves were off as Florida Sen. Marco Rubio, Texas Sen. Ted Cruz and GOP front-runner Donald Trump took jabs over immigration. Trump was accused of hiring undocumented immigrants, Rubio of going too light on immigration and Cruz of having a floppy record. Ohio Gov. John Kasich said he disliked how aggressive the debates had become.

Rubio and Cruz were asked about their Hispanic heritage and whether the Republican Party had lost a chance to mobilize Hispanic voters. Both said Republicans were the party for Hispanics, particularly because of their free-enterprise ideals. Rubio called it "the party of diversity."

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Republican presidential candidates Marco Rubio (left) and Donald Trump speak simultaneously at a debate in Houston, Feb. 25, 2016. Mike Stone/Reuters

"The Obama-Clinton economy has done enormous damage to the Hispanic community. It is not working in the Hispanic community," Cruz alleged.

UPDATE: 8:59 p.m. EST -- The debate started off with a question about immigration, directed to GOP front-runner Donald Trump, who Texas Sen. Ted Cruz has criticized for saying some undocumented immigrants would be allowed back in the U.S. after being deported. Trump responded, “They will come back, some, the best, through a process. They have to come back legally,” he said.

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Republican presidential candidates Sen. Marco Rubio, Donald Trump, and Texas Sen. Ted Cruz stand onstage Feb. 25, 2016, in Houston. Joe Raedle/Getty Images

Trump also claimed credit for bringing the issue of undocumented immigration into the campaign. The two took jabs at one another, as Cruz accused Trump of hiring undocumented immigrants. Ohio Gov. John Kasich called for practical solutions, vowing a pragmatic plan for addressing immigration.

Original story:

The final Republican debate before Super Tuesday on Thursday night in Houston promises to be an important evening for the remaining candidates. Missing from the stage will be former Florida Gov. Jeb Bush, once the presumed nominee, who dropped out earlier this week.

Billionaire Donald Trump will take center stage as the front-runner, after winning three Republican primary votes. Texas Sen. Ted Cruz and Florida Sen. Marco Rubio are hoping to prove they are viable candidates against Trump and are able to beat the Democratic nominee in November.

The debate comes after Trump won Nevada's Republican caucus Tuesday with 46 percent of the vote, followed in distant second by Rubio, with 24 percent, and Cruz with 21 percent. He’s heading confidently into the March 1 vote and has vowed it will be a smooth race.

"It's going to be an amazing two months," Trump said during his Nevada victory speech. "We might not even need the two months, folks, to be honest."

Rubio is aiming to shore up support among the GOP establishment, especially after Bush dropped out. Ohio Gov. John Kasich is struggling to spark excitement around his campaign, while Ben Carson has vowed to stay for the long haul, despite consistent low polling.

Kasich, who has been recognized for his more moderate views and calm demeanor, is hoping Thursday to generate some energy around his campaign. He had an impressive second-place finish in New Hampshire, but hasn’t seen much success since then. He’s now facing pressure to pull out of the Republican race so that Republicans can unite behind a candidate, offering a challenger to Cruz and Trump.

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Republican presidential candidates stand onstage before a debate in Greenville, South Carolina, Feb. 13, 2016. From left Sen. Ted Cruz of Texas, businessman Donald Trump and Sen. Marco Rubio of Florida. Daniel Acker/Bloomberg via Getty Images