Asked whether he would send special forces into Mexico to combat drug cartels, Gov. Ron DeSantis of Florida didn’t hesitate to swing for the fences.
“Yes, and I will do it on day one,” he said.
He pledged to declare a national emergency and added: “When these drug pushers are bringing fentanyl across the border, that is going to be the last thing they do. We are going to use force and leave them stone-cold dead.”
Republicans participating in the first presidential debate on Wednesday traded barbs and clashed repeatedly over abortion, climate change and how much fealty they owe to former President Donald J. Trump.
But, when it came to immigration, there was little disagreement, only efforts to outdo each other in offering aggressive recommendations for military responses to unauthorized immigration and drug trafficking across the southern border. The overwhelming majority of illicit substances are brought into the United States in commercial vehicles coming through official ports of entry, rather than by migrants, according to law enforcement.
Former Vice President Mike Pence did say that the United States would partner with the Mexican military, “and we will hunt down and destroy the cartels that are claiming lives in the United States.”
During the debate, there were almost no evocations of immigration as one of the triumphant strains in the American tapestry, just a steady drumbeat of menace. In part, that reflects the degree to which Donald Trump’s signature issue has become so ingrained in the Republican playbook and psyche.
But it also reflects the steady toll from drugs smuggled across the border, especially fentanyl, and the bitter trail of addiction and death that has stalked Americans across barriers of race, geography and class.
As a result, like so much else in Republican politics, proposals that were once fringe have become mainstream since Mr. Trump made the border a core issue of his 2016 campaign and, once elected, of his domestic political agenda.
Republican candidates in this campaign cycle have picked up his baton, embracing ideas that would have been deemed unthinkable before the Trump presidency.
For months, they have amped up their rhetoric about the southern border, raising the prospect of sending military troops to target drug cartels and stop what they call an invasion of migrants.
And polls show growing frustration among many demographic groups, including Democrats, about the influx of migrants, which has created chaotic scenes at the border in recent years and strained cities, from New York to Denver, where many of the arrivals have ended up.
But there are clear partisan divides, with two-thirds of Republicans saying that there should be fewer immigrants and asylum-seekers allowed into the country, compared to about a quarter of Democrats, according to an Associated Press poll earlier this year.
A poll by Gallup in July found that the percentage of Americans who believe immigration is a “good thing” is the lowest since 2014. The poll found a growing minority — 41 percent — of Americans believe immigration should be decreased, with Republicans far more likely to say so than Democrats. Still, a majority of Americans polled remain largely supportive of immigration and opposed to decreasing the number of immigrants.
The political fallout has been especially sharp in New York, where more than 100,000 migrants have arrived, with nearly 60,000 of those staying in shelters.
A poll released this week by the Siena College Research Institute found that large majorities of Democrats, Republicans and independents in both the city and upstate New York believe the migrants, many of them asylum-seekers, pose a “serious problem” for the state.
Roughly 46 percent of voters said that migrants resettling in New York in the last two decades have been more of a “burden” than a “benefit” to the state. Nearly 60 percent said that “New Yorkers have already done enough for new migrants and should now work to slow the flow” rather than “accept new migrants and work to assimilate them into New York.”
Unauthorized border crossings have declined in recent months, a result of measures that the Biden administration has introduced to enable people to enter the United States in a more orderly fashion, such as by making an appointment on a government mobile app for an interview with U.S. authorities at the border or being sponsored by a relative already in the country.
During Wednesday’s debate, the fentanyl crisis loomed large, with the candidates invoking overdose deaths as emblematic of the border crisis.
Senator Tim Scott of South Carolina called for firing 87,000 newly hired I.R.S. agents and doubling the number of border patrol agents. “The most pressing need of the American people is our southern border,” he said.
“If we spend $10 billion, we could finish the wall,” he said. “For $5 billion more, we could have the military-grade technology to surveil our southern border to stop the flow of fentanyl and save 70,000 Americans a year. “
Vivek Ramaswamy, who has called for securing the border by any means necessary, including with military force, said that resources the United States has been sending to Ukraine should be employed instead to “protect against the invasion across our southern border.”
Chris Christie, the former New Jersey governor, called for the detention of everyone entering the country unlawfully.
But in a rare sentiment respectful of immigration at the debate, he said, “We have so many wonderful people from around the world who are waiting in line following the law to try to come here and pursue the American dream. Those people are waiting and waiting and waiting because we haven’t dealt with the problem of the folks who are here.”
President Biden has repeatedly reminded Americans that only Congress can fix the broken immigration system. But, in an increasingly polarized political environment, prospects for a legislative solution backed by both parties have only become dimmer.