Christie criticized the idea that the president could cozy up to Vladimir Putin, noting that all recent presidents have failed to engage Putin by not being tough enough. He then hit Trump for having said that Putin was "brilliant and a great leader." As the night has worn on, Christie continues to be really the only candidate who is bothering to attack the guy who is 40 or more points ahead of every other candidate in national GOP primary polls.

— Analysis by Geoffrey Skelley of 538

Ilia Calderón is asking about sending U.S. troops to Mexico. In a late August/early September survey by Morning Consult, 41 percent of Republicans said they thought that sending U.S. troops to fight cartels in Mexico would be “very effective” at limiting the supply of illegal drugs in the United States. Other strategies had more support among Republicans, such as sending more resources to the U.S.-Mexico border (54 percent), empowering U.S. law enforcement to combat opioids (45 percent), and punishing drug violators in the United States (43 percent).
—Analysis by 538

Haley going after Ramaswamy was a recurring theme in the first debate. They were the standout candidates in our polling last time and there was a lot of speculation about Ramaswamy moving up in the polls — perhaps even surpassing DeSantis. But since August, Ramaswamy has actually lost support, to the point where Haley passed him in our polling average today. It makes sense that they're trading blows again; this seems to be a successful strategy for Haley, and Ramaswamy can't help but take the bait.
-Analysis by G. Elliott Morris of 538

The candidates are discussing support for Ukraine. About half (49 percent) of Republicans and Republican-leaning independents say that vital U.S. interests are not really at stake in the war in Ukraine, according to an August Echelon Insights survey. Thirty-seven percent disagree, saying that if Russia wins, vital U.S. interests and values are threatened. Fourteen percent are unsure.
—Analysis by 538

Several of the Republicans on stage touted their prioritization of border security should they win the presidency.

“What I’ll do on day one is sign an executive order to send the National Guard to partner with Customs and Border Patrol to make sure that we stop the flow of fentanyl over the border,” Christie said first. He expanded his answer to include his plans to fill the “6 million vacant jobs” in the country with legal immigrants.

“This border is going to be a day one issue for me as president,” DeSantis said, also noting that he’d administer the remain in Mexico policy, which requires migrants seeking asylum to remain in Mexico until their US immigration court date.

“We're going to declare a national emergency. Yes, we'll build the wall. We’ll do remain in Mexico,” DeSantis said.

Pence spoke about his role in negotiating the remain in Mexico policy of the Trump administration.

“I negotiated the remain in Mexico policy with the Mexican government. We used economic power to bring the Mexican government to the table. We build hundreds of miles of border wall and despite what's said here today, we reduced illegal immigration and asylum abuse by 90%. And as President of the United States, I can do it again,” he said. “I'm going to be ready on day one to get Congress to step up, secure the southern border of the United States.”

Haley cosigned on the Remain in Mexico Policy.

“Let's go back to Remain in Mexico policy,” she said. “Instead of catch and release. Let's go to catch and deport.”
Ramaswamy said that he was supportive of most of his opponents’ border positions, but that he’d go a step further: he’d end birthright citizenship for the kids of illegal immigrants.

“The Republicans on the stage are on the right side of this issue, militarize the southern border, stop funding sanctuary cities and end foreign aid to Mexico and Central America to end the incentives to come across,” Ramaswamy said.

--ABC News' Isabella Murray