5 Moments That Mattered at the Houston Republican Presidential Debate

— -- At the final Republican presidential debate before Super Tuesday, the knives were drawn and the three candidates with the best chance of capturing their party’s nomination -- Donald Trump, Marco Rubio and Ted Cruz -- were out for blood.

In particular, Trump and Rubio, two candidates who pulled their punching in other outings, slashed each other tonight in exchange after exchange. Cruz took some swipes at the GOP front-runner too. Meanwhile, the other two candidates on stage -- John Kasich and Ben Carson -- seemed like supporting actors.

Here are five moments that mattered on Thursday night:

1. Rubio Rattles Trump

If you were wondering who would fill Jeb Bush's shoes and take on Donald Trump at tonight’s debate, the answer came right out of the gate: Marco Rubio.

The first issue was immigration and a report that Trump employed undocumented immigrants.

“If you're going to claim that you're the only one that lifted this into the campaign, that you acknowledge that, for example, you're the only person on this stage that's ever been fined for hiring people to work on your projects illegally,” Rubio said.

Trump shot back: “I’m the only one on the stage that’s hired people.”

Ted Cruz also joined Rubio in going after Trump. “When I was leading the fight against the gang of eight amnesty bill, where was Donald? He was firing Dennis Rodman on ‘Celebrity Apprentice,’” Cruz quipped.

2. The Great Wall of Trump

Donald Trump defended his proposal for a new wall on the southern border of the United States, blasting former Mexican president Vicente Fox for rebutting the idea that Mexico would pay for the wall.

"The wall just got 10 feet taller, believe me," Trump said.

Fox had said the country is "not paying for that f------ wall."

Trump took direct aim at Fox's language, despite his own personal use of profanity. "I can only tell you, if I would have used even half of that word, it would have been a national scandal," he said.

Trump has not yet released any specific plans for funding or building the wall.

3. Ben Carson’s Fruit Salad

One of the important issues at tonight’s face-off was how the candidates would choose a Supreme Court justice.

“And as president, I will go through and I will look at what a person's life has been,” Carson said. “That will tell you a lot more than an interview will tell you. The fruit salad of their life is what I will look at.”

Ted Cruz promised his nominee would be conservative. “I give you my word, every justice I nominate will vigorously defend the bill of rights for my children and for yours,” Cruz said.

Trump surprisingly defended Planned Parenthood, although he did say he would defund it.

“I'm totally against abortion having to do with Planned Parenthood, but millions and millions of women -- cervical cancer, breast cancer -- are helped by Planned Parenthood,” the Republican front-runner said.

Carson, who was largely absent from the debate, asked at one point, “Can somebody attack me, please?”

4. But I Repeat Myself

Several weeks ago, Chris Christie attacked Marco Rubio for consistently reciting his “25-second memorized speech.”

Now, Rubio has taken that attack line and used it on Donald Trump.

“Now he’s repeating himself,” Rubio said when Trump started talking about how he would have many different health care plans. Clearly flustered, Trump replied, repetitiously, “I don't repeat myself. I don't repeat myself.”

Trump then referenced Rubio’s showdown with Chris Christie in New Hampshire, claiming Rubio “melted like a swimming pool.”

Once again, Rubio had a comeback. “He says five things: everyone's dumb, he's going to make America great again. Win, win, win. He's winning in the polls. And the lines around the states. Every night,” Rubio said.

5. Trump and Taxes

While Cruz went on the attack over Trump’s reluctance to release his tax returns, Trump defended himself by saying he’s been audited annually for over a decade.

“He can release past year tax returns, he doesn't want to do it,” Cruz said. “If there's nothing, release them tomorrow,” Cruz said, pointing to pending litigation over Trump University.

But Trump pointed to several years of audits on his taxes.

“I'm being audited,” he said. “It's a very routine audit and it's very unfair because I've been audited for I think over 12 years, every year because of the size of my company.”