For months, the Florida senator resisted taking on Republican front-runner and expert attack dog Donald Trump, much to the chagrin of the GOP establishment. That reluctance evaporated during the final GOP presidential debate before Super Tuesday.

Standing to the right of Trump, Rubio delivered one blow after another at the billionaire businessman, attacking him on everything from immigration to foreign policy and health care to the businessman's hiring practices. And to Trump's left, Ted Cruz delighted in joining in the pile-on.

In the middle of a debate filled with fireworks and filled with barely audible exchanges in which the three candidates furiously talked over one another, Trump pointed to the two men flanking him and lashed out: "This guy is a choke artist," he said, turning to Rubio, "and this guy's a liar," he said of Cruz.

Watching it all from the audience was former President George H.W. Bush and his wife, Barbara, whose era of politics seems long gone in today's Republican Party. Their attendance was all the more notable since this was the first GOP debate of the season in which their son, Jeb, didn't appear after dropping out of the race.

Rubio's change in tone came just five days ahead of a slew of March 1 primary contests, when hundreds of delegates will be up for grabs. The evening marked the strongest debate performance for the Florida senator, who immediately used a question about immigration to aim fire at Trump.

"You're the only person on this stage that's ever been fined for hiring people to work on your project illegally," Rubio told Trump.

Rubio and Trump spoke over each other as the senator accused the real estate mogul of hiring Polish workers. Trump dismissed the episode as something that happened decades ago.

"I guess there's a statute of limitations on lies," Rubio retorted.

Photos: Who's running for president? Photos: Who's running for president? Ted Cruz, Donald Trump, John Kasich, Hillary Clinton and Bernie Sanders, Hide Caption 1 of 6 Photos: Who's running for president?



"So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Businessman Donald Trump announced June 16 at his Trump Tower in New York City that he is seeking the Republican presidential nomination. This ends more than two decades of flirting with the idea of running for the White House."So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Hide Caption 2 of 6 Photos: Who's running for president?



"These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Sen. Ted Cruz of Texas has made a name for himself in the Senate, solidifying his brand as a conservative firebrand willing to take on the GOP's establishment. He announced he was seeking the Republican presidential nomination in a speech on March 23."These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Hide Caption 3 of 6 Photos: Who's running for president? Ohio Gov. John Kasich joined the Republican field July 21 as he formally announced his White House bid.



"I am here to ask you for your prayers, for your support ... because I have decided to run for president of the United States," Kasich told his kickoff rally at the Ohio State University. Hide Caption 4 of 6 Photos: Who's running for president?



"Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hillary Clinton launched her presidential bid on April 12 through a video message on social media. The former first lady, senator and secretary of state is considered the front-runner among possible Democratic candidates."Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hide Caption 5 of 6 Photos: Who's running for president?



"This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Sen. Bernie Sanders , an independent from Vermont who caucuses with Democrats, announced his run in an email to supporters on April 30. He has said the United States needs a "political revolution" of working-class Americans to take back control of the government from billionaires."This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Hide Caption 6 of 6

Rubio later mocked Trump for having a "fake school," referring to lawsuits aimed at Trump University alleging fraud and deception.

Trump hit back: "Here's a guy that buys a house for a $179,000 -- he sells it to a lobbyist who's probably here for $380,000."

Rubio responded by calling out Trump for his privileged background.

"If he hadn't inherited $200 million, you know where Donald Trump would be right now? Selling watches in Manhattan," Rubio said.

Rubio also challenged Trump on foreign policy.

Trump repeatedly stated his support for Israel, billing himself the most "pro-Israel" candidate in the GOP field. But even as he said he was "totally pro-Israel," he also said he didn't believe there was any reason for labeling Israel and the Palestinians as the "good guy" and the "bad guy."

"The position you've taken is an anti-Israel position," Rubio said.

JUST WATCHED Rubio to Trump: 'Palestinians aren't a real estate deal' Replay More Videos ... MUST WATCH Rubio to Trump: 'Palestinians aren't a real estate deal' 00:55

When Trump said he was simply a "negotiator," Rubio shot back: "The Palestinians are not a real estate deal, Donald."

Clashing on health care

One of the most explosive exchanges between Trump and Rubio came when the candidates were asked to discuss their health care plans.

Trump said he would get rid of barriers between the states --- something that he argued would increase competition. Rubio repeatedly pressed his rival for more details. "What else is a part of your health care plan?"

"When you get rid of the lines, that brings in competition," Trump said.

"Now he's repeating himself," Rubio responded.

"I don't repeat myself. Here's the guy who repeats himself," Trump shot back, referring to Rubio. "I watched him repeat himself five times four weeks ago."

Rubio, appearing amused, quipped: "I saw you repeat yourself five times five seconds ago!"

The senator also accused Trump of reusing the same general points on the campaign trail: "Everyone's dumb, he's going to make America great again, he's gonna win win win, he's winning in the polls."

CNN's Dana Bash cut in to ask whether Trump has any more to add to his previously stated proposal on health-care reform.

"No, there's nothing to add. What's to add?" Trump said.

Cruz also went on the offensive, saying Trump had previously donated to Democrats who had worked on the so-called Gang of Eight immigration reform bill. Voters should judge a candidate by looking at their "record before they were a candidate for president," Cruz added.

The conservative firebrand senator won the Iowa caucuses but has not been able to notch another victory since, and has been forthright about the ramifications of Super Tuesday, especially the significance of his home state of Texas, where there are 155 delegates at stake.

A Monmouth University poll released Thursday put Cruz 15 points ahead of Trump in Texas.

Trump's taxes

Mitt Romney, the 2012 GOP presidential nominee, also played a role in the debate. He sparked controversy Wednesday when he suggested Trump's tax returns could contain a potential "bombshell" and urged the businessman to release his information.

JUST WATCHED Romney predicts 'bombshell' in Trump's taxes Replay More Videos ... MUST WATCH Romney predicts 'bombshell' in Trump's taxes 00:48

On the debate stage, Trump claimed that is being audited and that he would not release the returns until that process was over.

"I can't release it while I'm under an audit," he said.

Cruz echoed Romney's suggestion that there may be something problematic lurking in Trump's tax returns.

"Donald Trump says he's being audited. I would think that would underscore the need to release those returns," he said. "He doesn't want to do it because presumably there is something in there that's bad."

Cruz and Rubio said they would release new tax returns within the next two days.

Supreme Court battle

Cruz and Rubio also tussled with Trump over replacing Supreme Court Justice Antonin Scalia.

When Cruz vowed to nominate principled constitutionalists to the bench as president, Trump shot back: "Justice (John) Roberts was strongly recommended and pushed by Ted."

"Justice Roberts gave us Obamacare. Might as well be called Robertscare," Trump said. "That is a rough thing and I know Ted feels badly about it."

Cruz slammed Trump for donating to Democrats in the past — a sign, Cruz warned, that Trump would get to Washington and "cut a deal" on Supreme Court appointees.

Trump responded by blasting Cruz for being an obstructionist in Congress — "You have to have somebody who can make deals," he said.

Responding to Fox

Trump also responded to former Mexican President Vicente Fox's recent response to Trump's claim that Mexico would pay for his proposed U.S.-Mexico wall.

"I'm not going to pay for that f***ing wall. He should pay for it," Fox told Fusion's Jorge Ramos in an interview published Thursday.

On the CNN debate stage, Trump retorted: "The wall just got 10 feet taller."

"I saw him make the statement. I saw him use the word that he used," Trump added. "This guy used a filthy, disgusting word on television ... He should apologize."