Tonight's Republican debate in Houston was a rollicking affair where Texas Sen. Ted Cruz and Florida Sen. Marco Rubio double-teamed businessman and frontrunner Donald Trump over the course of two-and-half hours.

"We're having a lot of fun up here tonight, I have to tell you," Trump said toward the end of the night.

1. Despite predictions that he would play nice with The Donald, Rubio went after Trump immediately

CNN

There was a lot of speculation about whether Rubio would take on Donald Trump at tonight's debate, but he ended that speculation immediately when he accused Trump of hiring foreign workers on his real estate development projects. Rubio referenced the fact that Trump's company was sued in 1983 for hiring (and not fairly compensating) 200 undocumented Polish workers to clear the land that was later used to build the Trump Tower in New York. (The case was eventually settled. For more on what happened, read Michael Daly's piece at the Daily Beast.)

"If he builds the wall the way he built Trump Towers, he will be using illegal immigrant labor to do it," Rubio said.

Cruz also got in on the fun of this line of attack.

"Anyone who cared about illegal immigration wouldn’t be hiring illegal immigrants," Cruz said about Trump.

Trump responded by saying that he only resorted to undocumented workers because there were no Americans available to do the work. He also accused Rubio of not understanding business.

"I’m the only one on this stage that has hired people," Trump said to Rubio. "You've hired no one."

You can watch the whole exchange here:

2. Rubio also called out Trump's family wealth

CNN

Perhaps in an attempt to appeal to the blue collar workers supporting Trump's campaign, Rubio pointed out that Trump inherited a significant amount of money to start his businesses.

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

Trump responded by saying that he only took one million dollars from his father.

3. Cruz took shots at Trump's past support of liberal Democrats

Cruz's shots came at Trump from the right, where he tried to paint Trump as an unreliable conservative. He pointed out that Trump has donated money to liberal Democratic politicians, such as Vice President Joe Biden and former Speaker of the House Nancy Pelosi. Cruz argued that Trump's inconsistent conservatism meant that he could not be trusted by Republican voters to nominate conservative justices to the Supreme Court.

4. Trump took some heat tonight for repeating himself

CNN

In the last debate before the New Hampshire primary, Rubio infamously repeated the same line over and over in the face of an attack by Gov. Chris Christie. Tonight, Rubio got the chance to call someone robotic, and his target was Trump. The topic of discussion was the candidates' health care proposals, and Rubio jumped on Trump's plan to eliminate regulation that prevents the selling of health insurance across state lines.

"We should have gotten rid of the lines around each state so we could have real competition," Trump said.

But when Rubio pushed Trump on elaborating on that point, asking if "that's the only part of the plan," Trump once again brought up state lines.

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

"I watched him repeat himself five times," Trump responded.

"I saw you repeat yourself five times, five seconds ago," Rubio then said to applause.

It should be noted, however, that Rubio never really got around to explaining his own plan to replace Obamacare.

You can watch the full exchange here:

Rubio and Cruz attacked Trump because they're behind.

Google

There's no doubt that Trump has the inside track to win the nomination at this point. For one, he won the last three Republican nomination contests — in New Hampshire, South Carolina, and Nevada. He's also enjoying good polling in Texas and Florida, the home states of Cruz and Rubio, respectively. (Texas votes on Super Tuesday on March 1; Florida goes to the polls on March 15.) In Texas, one poll has Trump and Cruz tied. In Florida, the latest poll shows Trump with a healthy 16-point lead on Rubio.

That's why this is a do or die situation for Cruz and Rubio. It's unlikely that Rubio can mount a comeback against Trump without winning Florida. And it's even less likely that Cruz can make up ground on Trump without winning Texas.

So who won?

While Cruz did have his moments, it was clear that Rubio was prepared to stand up to Trump tonight, and he succeeded. Rubio went a long way toward showing that he's the man to beat Trump, something that many mainstream Republicans have been waiting to see since Trump first took the lead in polling last summer. There have been nine Republican debates before tonight, and Rubio was the first to consistently draw blood against Trump and get under his skin throughout the night.

Will it be enough? We'll see if Rubio makes up some ground on Super Tuesday in five days when 12 states host primaries.