DeSantis said the U.S. Navy isn't large enough and he'd expand it significantly to meet China's threats. Right now, the U.S. Navy has 291 ships but DeSantis says his plan would be 385 ships by the end of two terms.

The Florida governor compared the threat of China today to the threat of the Soviet Union post-World War II, warning a Chinese superpower would want to "export authoritarianism" around the world.

"I think the future of freedom is going to be determined in the Indo-Pacific," he said. "We have a strategy not just with military but decoupling from the economy and fighting them here at home."

He then went after Haley for recruiting Chinese companies to invest in South Carolina when she served as governor, while he's worked to ban Chinese citizens from buying land in Florida.

-ABC News' Alexandra Hutzler

Americans once had fairly mixed views of China, but they have become far more negative in the past five or so years, based on data from the Pew Research Center. In 2018, 47% of Americans had an unfavorable view of China while 38% had a favorable one. But that unfavorable percentage shot up to 60% in 2019 and it's only risen further since -- a whopping 82% said they had an unfavorable view in 2022. The national security and foreign policy attacks that Republican candidates have made on China in this debate likely resonated, although Americans tend not to list overseas concerns as a top worry.

-Analysis by Geoffrey Skelley of 538

Scott, Haley and Christie sounded support for Ukraine against Russia while Ramaswamy and DeSantis were more skeptical of how much Washington should back Kyiv.

"We have been very effective using our resources and our weaponry and the very high price of Ukrainian blood to achieving that objective," Scott said of degrading Russia's military.

Still, Scott argued, "The American people are frustrated that they do not have a president who reminds us and tells us where's the accountability -- how are those dollars being spent? We need those answers for us to continue to see the support for Ukraine."

Haley said she does not support handing Ukraine cash but that the U.S. should "give them the equipment and the ammunition to win."

Christie, meanwhile, argued support for Ukraine "is the price we pay for being leaders of the free world."

Ramaswamy, who has hammered Ukraine throughout his campaign, called Ukraine corrupt.

"To frame this as some kind of battle between good and evil, don't buy it," he said.

DeSantis, meanwhile, sought to pivot to immigration but said, "We are not going to send your sons and daughters to Ukraine."

-ABC News' Tal Axelrod

Ramaswamy is different from his colleagues when it comes to Ukraine, generally arguing that the United States pull away from Ukraine’s fight against Russian invaders.

“Ukraine is not a paragon of democracy,” Ramaswamy said. “This is a country that has banned 11 opposition parties.”

His point about political parties is accurate, but it needs context.

Ukraine banned 11 pro-Russian parties -- the largest of which occupied 44 out of 450 seats in Ukraine's Parliament, according to Radio Free Europe. The party’s leader, Viktor Medvedchuk, is aligned with Russian President Vladimir Putin. Putin is the godfather of Medvedchuk's daughter, Radio Free Europe reported.

-Analysis by Aaron Sharockman of PolitiFact

Not far from where his rivals are gathering in Miami, Trump is hosting a rally in Hialeah, a heavily Hispanic part of Florida where Republicans have seen gains in recent years.

It's his third straight time bucking the debates, even though he's easily met the polling and donor thresholds.

The former president and his team are ditching the events in a signal that, to them, the primary is essentially already over -- which his challengers reject -- and he's refusing to sign the Republican National Committee's loyalty pledge vowing to support the ultimate GOP nominee regardless of who it is.

-ABC News' Tal Axelrod