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

The second debate stage will look mostly like the first, as seven of the eight candidates who took part in the initial August debate qualified for tonight’s event. And just like the first debate, front-runner Trump has decided to skip the event, despite having the polls and donors to make it. To qualify, the RNC mandated that candidates have at least 3 percent support in two national polls, or at least 3 percent in one nationwide survey and two polls from separate early states, based on polls conducted since Aug. 1 that met the RNC’s criteria for inclusion. Candidates also had to attract at least 50,000 unique contributors, with at least 200 from 20 different states or territories.

The RNC raised the polling and donor standards for the second debate, which slightly winnowed the list of participants. The new rules raised the level of support candidates needed in qualifying polls from 1 percent to 3 percent, and the number of unique donors from 40,000 to 50,000. Six of the seven qualifying candidates had little trouble meeting these polling and donor thresholds. However, although Burgum had enough donors, he struggled to poll well enough nationally to qualify. It took until the Saturday before the debate for him to get the national poll at 3 percent he needed. Meanwhile, former Texas Rep. Will Hurd and former Arkansas Gov. Asa Hutchinson came up short of qualification, as Hurd lacked sufficient polls and only got to 50,000 donors on Monday, while Hutchinson didn’t have enough qualifying polls or donors.

—Analysis by Geoffrey Skelley of 538