Donald Trump has reiterated his pledge during Tuesday's (local time) Republican presidential debate to deport millions of undocumented workers.
It is a plan trashed by rivals including Jeb Bush, who warned overzealous anti-immigrant sentiment would be a gift to Democrats.
"We will have a wall. The wall will be built. The wall will be successful," Trump, the Republican frontrunner and real estate tycoon, said about the partition he has vowed to build on the southern US border with Mexico.
Asked directly by a moderator if he would deport five million immigrants, Trump said, "You will have to send people out."
But he refused to explain what effect he thought such mass deportations would have on the US economy.
"We're a country of laws. We either have a country or we don't have a country," he said.
The issue surfaced in the party's fourth debate of the 2016 primary cycle one day after a federal appeals court blocked measures announced by US President Barack Obama last year that would give work permits and deportation protection to more than four million undocumented migrants.
Bush stepped in to warn that sending back half a million immigrants per month "is just not possible".
"It's not embracing American values, and it would tear communities apart, and it would send a signal that we're not the kind of country that I know America is."
Bush, who boasts proudly of the bicultural family he has created with his wife, who is from Mexico, has been pilloried by rivals as the Republican candidate most open to immigration reform.
But he warned against turning residents out of their homes and sending them back across borders, saying it "sends a powerful signal" to voters and to Democratic White House hopefuls like Hillary Clinton.
"They're doing high-fives in the Clinton campaign right now when they hear this," he said.
"What we need to do is allow people to earn legal status."
Ohio Governor John Kasich, a comparative moderate on the stage, dismissed Trump's plans as wrongheaded.
"We all know you can't pick them up and ship them back across the border," he said. "It is a silly argument, it is not an adult argument."