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

Tonight I’ll be keeping track of DeSantis, who, despite several campaign shakeups and a steady slide in both national polls and early state surveys remains the second-place contender in the GOP primary, and who will appear at center stage this evening. DeSantis didn’t have a breakout moment last debate, though he may have been hobbled by the embarrassment of his Super PAC publicly releasing his entire debate strategy just beforehand. This time around, he may need to make a larger splash to re-convince voters he’s the best (or only) alternative to Trump. The other candidates are now nipping at his feet — he’s not even polling second in New Hampshire and South Carolina anymore — and if he becomes just another member of the pack he could lose whatever luster he has left. He’s already (started taking shots at Haley)[], who had one of the better-reviewed first debate performances and who has seen some movement in the polls. With seven candidates on stage, he’ll have limited time to make his move. Will he finally go after Trump more forcefully, or does he feel enough pressure from below to focus on Haley and the others?

—Analysis by Jacob Rubashkin, 538 contributor