7 key moments from the Republican presidential debate

The first Republican presidential debate offered an opportunity for the top 10 candidates to introduce themselves to a national audience — and test their patience with Donald Trump at center stage.

The debate, sponsored by Fox News and Facebook, featured feisty exchanges over abortion, the National Security Agency, Hillary Rodham Clinton as a general election opponent and the Iran nuclear deal.

Here are seven critical moments from the most consequential day yet in the 2016 Republican presidential race:

1. When Donald Trump raised his hand

Talk about an interesting start. With the very first question, the Fox News moderators targeted Trump without saying his name. Bret Baier asked this: Would any candidates unwilling to pledge their support to the GOP nominee and not run as an independent raise their hand?

Trump — the only candidate to raise his hand on stage — took the bait.

The audience jeered, and Trump turned his bombast down a notch momentarily. But question after question, Trump appeared less like an electable candidate in a GOP primary. It began with this moment in the first minute.

2. Megyn Kelly asks Trump about his disparaging comments on women

Trump's contentious battle with the moderators continued when Fox News host Megyn Kelly asked him about his "disparaging comments about women's looks."

"You've called women you don't like 'fat pigs, dogs, slobs, and disgusting animals,'" Kelly said.

"Only Rosie O'Donnell," Trump replied to audience laughs.

"For the record, it was well beyond Rosie O'Donnell," Kelly clarified, referring to remarks on his Twitter account.

Trump then took a swing at Kelly, but she had already hit it out of the park.

3. The Christie-Paul Fracas

Early in the evening, Governor Chris Christie of New Jersey and US Senator Rand Paul of Kentucky got into a heated exchange over terrorism and the role of the NSA.

Paul, an outspoken libertarian, charged Christie, a former US attorney, to "use the Fourth Amendment" and "Get a judge to sign the warrant!" to collect data on potential terrorists.

Then, in one of his most prominent moments of the evening, Christie told Paul, "Listen, senator, you know, when you're sitting in a subcommittee, just blowing hot air about this, you can say things like that."

The verbal brawl served both candidates well, but Christie showed better overall during the evening. After narrowly qualifying for this debate, Christie won by going toe-to-toe with his party nemesis.

4. Marco Rubio compares his life story to Hillary Clinton

US Senator Marco Rubio, of Florida, had probably the best performance of the night out of anyone on stage. It began with a question about his political experience in Florida compared to his one-time friend and now rival, former governor Jeb Bush.

In one of many examples of his adeptness Thursday evening, Rubio responded the presidential election is not "a resume competition" and turned his target instead to Clinton.

"If I'm our nominee, how is Hillary Clinton going to lecture me about living paycheck to paycheck?" Rubio said. "I was raised paycheck to paycheck. How is she -- how is she going to lecture me -- how is she going to lecture me about student loans? I owed over $100,000 just four years ago."

5. 'Sell them like they're parts to a Buick'

Former Arkansas governor Mike Huckabee was known for his folksy populism during his 2008 run for president. In 2016, he's better known as a stringent social conservative.

The moderator, Chris Wallace, asked Huckabee about how that would appeal to Democrats and Independents in a general election. Huckabee quickly pivoted to his anti-abortion beliefs, with a nod to the popular rhetoric of his former campaign — a blend of both candidacies.

"It's time that we recognize the Supreme Court is not the supreme being, and we change the policy to be pro-life and protect children instead of rip up their body parts and sell them like they're parts to a Buick," Huckabee said.

6. John Kasich declines to hit Trump

From the start of the debate, it was clear Paul wanted to take on Trump. Within minutes, Paul charged Trump with "hedging his bet on the Clintons," resulting in a terse exchange with the businessman.

So it was just as interesting when Ohio Governor John Kasich took a pass on prodding Trump later in the debate. At the same time, Kasich attempted to appeal to Trump's supporters without sounding like a sycophant.

"Donald Trump is hitting a nerve in this country. He is. He's hitting a nerve," Kasich said. "People are frustrated. They're fed up. They don't think the government is working for them. And for people who want to just tune him out, they're making a mistake."

7. Scott Walker tackles foreign policy in the Middle East

Walker's detractors argue he's not ready for prime time, especially on foreign policy. Fox News challenged him to name one country in the Middle East with which he would want to improve the country's relations.

Walker dodged it. (Suggestion from the peanut gallery: Turkey.)

More importantly, Walker's answer symbolized just how little he factored into the GOP debate.

Along those lines, one other top candidate didn't make many memorable moments in Thursday's debate either: Bush.