Nine candidates took part in the Republican debate yesterday in Las Vegas, including frontrunner Donald Trump and his rival Jeb bush, and senators Marco Rubio and Ted Cruz.
Terrorism and national security were big topics dominating the discussion, while a series of jabs were made at Trump by the other participants.
Here's who said what on some of the main topics:
There discussion around the National Security Agency's surveillance programme, particularly relating to how it could tackle Islamic State militants.
In support of greater surveillance powers, Mark Rubio said: "Here's the world we live in. This is a radical jihadist group that is increasingly sophisticated. We are at a time when we need more tools, not less tools."
Then, taking a swipe at Ted Cruz, who had voted in favour of limiting surveillance powers, he said: "If terrorists strike again... the first question will be, 'Why didn't we know about it and why didn't we stop it?'"
Trump's call to “ban Muslims”
Trump recently called for a ban on all Muslims from entering the US, which caused significant backlash.
Trump tried to defend himself yesterday by saying: "We are not talking about religion, we are talking about security."
But his main rival Jeb Bush said this, along with his proposal to go after the family members of terrorists, was an “example of Trump's lack of seriousness”.
He also told Trump: "You're not going to be able to insult your way to the presidency.”
In retaliation, Trump said “give me a break”, adding: “I think Jeb is a very nice person, [a] very nice person. But we need toughness."
Previously, Trump said he would like to “close that internet up” to stop Islamic State recruiting.
"I don't want them using our internet,” he said.
Focusing on that comment, Rand Paul said: “The question is, how do we keep America safe from terrorism? Trump says we ought to close that internet thing. The question really is, what does he mean by that? Like they do in North Korea? Like they do in China?”
Trump reacted by saying: “So, they can kill us, but we can't kill them? That's what you're saying. And as far as the internet is concerned, we're not talking about closing the internet. I'm talking about parts of Syria, parts of Iraq, where Isis is, spotting it.”
Now, you could close it. What I like even better than that is getting our smartest and getting our best to infiltrate their internet, so that we know exactly where they're going, exactly where they're going to be. I like that better.
Ted Cruz attacked Mark Rubio for his involvement in the “Gang of Eight” immigration reform bill, which eases laws on some foreigners trying to gain residency in the US.
Cruz described it as a “massive amnesty plan”, and he also accused Rubio of working alongside the Democrats to give it “blanket authority” to accept refugees.
"He was fighting to grant amnesty and not to secure the border. I was fighting to secure the border," he said.
Rubio reacted by criticising Cruz's support of the H1-B visa programme, which encourages immigration of skilled workers into the country.