DeSantis expressed support for using the U.S. military to combat drug cartels across the border.

"The president of the United States has to use all available powers as commander in chief to protect our country and the people," DeSantis said.

"When they are coming across, yes we are going to use lethal force," he continued -- a line he's used repeatedly throughout the campaign.

Activists have pushed back that his plan is inhumane and illegal.

-ABC News' Alexandra Hutzler

Martha MacCallum just asked about what to do about migrants already in the United States. In a July poll by The New York Times/Siena College, 39 percent of likely Republican voters say that they supported a “comprehensive immigration reform bill that provides a pathway to citizenship for all undocumented immigrants” in the United States, while 57 percent opposed such a bill. Support was weakest among Trump supporters (29 percent) compared with DeSantis supporters (48 percent) and voters who say they will vote for another candidate (50 percent).
-Analysis by FiveThirtyEight

While many candidates onstage have sparred with each other -- including Haley and Ramaswamy swapping sharp words on foreign policy -- Scott has yet to engage with any of the other candidates.

Much of his remarks have almost word for word repeated elements from his campaign stump speech. When asked about China, which he has addressed in other appearances, he pivoted to speaking about the U.S. border.

-ABC News’ Gabriella Abdul-Hakim and Oren Oppenheim

Asked to raise their hand if they would not increase aid to Ukraine, DeSantis did so, saying that "Europe needs to step up. They need to step up and do their job."

He argued: "I would have Europe pull their weight. ... Our support should be contingent on them doing it.

DeSantis -- who had received backlash from some other politicians for seemingly backtracking on support for Ukraine -- pivoted to say that he wasn’t going to send troops overseas but rather down to the Southern border.

-ABC News' Hannah Demissie and Will McDuffie

One challenger to Trump has surged ahead — in ad buys, at least. Scott announced an $8 million ad buy this month. The bulk of that, $6.6 million, will go toward TV advertisements in early primary states Iowa and New Hampshire, according to the Washington Post. That’s on top of the $40 million ad buy planned by a super PAC supporting Scott that was announced last month.

Trump and DeSantis, the two front-runners, had dominated in early ad spending. But challengers like Scott have stepped up as they’ve tried to qualify for debates and raise name recognition in early voting states. Super PACs supporting Haley and Burgum have also increased spending recently. Stand for America Fund, Inc., which is aligned with Haley, spent $2.3 million on ads so far in August, while Best of America, which backs Burgum, has spent $2.1 million, according to reporting from NBC News.

Meanwhile, Trump-supporting PACs have spent millions on the former president’s legal fees as the number of indictments filed against him has risen to four. That will leave less money for spending on ads going forward, but Trump remains the top campaign fundraiser.

-Analysis by Monica Potts of FiveThirtyEight