Donald Trump clashed with rivals, former Florida governor Jeb Bush and Ohio governor John Kasich in the Republican Party's fourth presidential debate over his controversial proposal to deport 11 million illegal immigrants.
The Republican frontrunner, whose anti-immigrant rhetoric has found favour with conservatives, repeated his plan to build a wall along the border with Mexico to keep immigrants out and to mass-deport "undocumented" migrants.
Kasich, who is vying with Bush for the support of Republican establishment voters, rubbished Trump’s plans as being unrealistic.
“Think about the families; think about the children. Come on folks, we know you can’t pick them up and ship them across the border. It’s a silly argument. It’s not an adult argument,” said Kasich, who is running seventh in the polls.
Trump shot back with an earlier putdown, dismissing Kasich’s economic resurgence. “You’re lucky in Ohio you struck oil,” he said.
As they sparred on the issue, the billionaire property tycoon and reality TV star snapped: “I built an unbelievable company worth billions and billions of dollars - I don’t have to listen to this man,” drawing boos from the audience in Milwaukee.
The exchange was one of the sharpest of the latest TV contest, which was hosted by the Fox Business television network and focused on economic matters.
The debate also touched on national security as the candidates presented their conservative credentials to primary voters with 82 days until the Iowa caucuses, the first candidate-nominating contest in the 2016 presidential race.
Bush rowed into the fiery debate on immigration after Trump urged moderators to "let Jeb speak," bringing laughter from the Wisconsin crowd.
He thanked Trump for allowing him to speak and for his generosity, and proceeded to rubbish the mogul’s immigration plan as “not possible.”
“It would tear communities apart and it would send a signal that we’re not the kind of country I know America is,” said Bush, who is fifth in the polls.
“They’re doing high fives in the Clinton campaign right now when they’re hearing this,” he added.
Moderators challenged the eight top-polling candidates who made the main-stage debate on their policies in contrast to the previous debate where moderators on the CNBC business network were criticised for tabling “gotcha” questions.
Some questions were, however, seen as being soft on the candidates, particularly on the retired neurosurgeon, Dr Ben Carson, the second-highest polling candidate who trails Trump by just two percentage points.
Carson, whose personal story of redemption from angry youth to talented doctor has been shown up by the media with inconsistencies in parts, poked fun at the press’s interest in his life going back decades when asked about it.
“Well, first of all, thank you for not asking me what I said in the 10th grade,” he said, to laughter to the crowd.
Media vetting of presidential candidates was a "good thing," he said, but pointed to double standards in the media, noting that Democratic presidential favourite Hillary Clinton had not been subjected to the same scrutiny.
“I have no problem with being vetted,” he said. “What I do have a problem with is being lied about and then putting it out there as truth. I don’t even mind that so much if they do it with everybody.”
Carson and Trump were largely outshone on the night as the establishment candidates debated the nitty gritty of economic and foreign policy, though that has not hurt the two frontrunners’ poll numbers in the past.
"Why does she keep interrupting?" the abrasive Trump said at one point in response to former Hewlett Packard chief executive Carly Fiorina, the only female Republican candidate who put in an assured performance.
Florida senator Marco Rubio, the surging candidate of recent weeks rising to third in the polls, locked horns with Kentucky senator Rand Paul on military spending calling him "a committed isolationist."
Senator Paul put in his best debate performance of the campaign, setting out his libertarian views on foreign policy with confidence, saying Rubio could be “a conservative and be liberal on military spending.”
Texas senator Ted Cruz, an anti-establishment figure in Washington, debated strongly too, though at one point he counted the Department of Commerce twice when listing the five government agencies he would shut down as president.
The gaffe cast memories back to Rick Perry’s famous “oops” moment and a similar mix-up in a 2011 debate that cost him his presidential bid.
In a heated back-and-forth on bank bailouts, Kasich drew boos from the crowd with a confused explanation about how he would not bail out big banks but ensure that depositors are protected.
His interruptions at times came across as hectoring and patronising as he looked to play up his “executive” experience and make a mark in the 2016 race.
In one of the stranger references of the night, Rubio, outlining his opposition to a raise in the minimum wage, said he couldn’t understand why vocational education was stigmatised when it could lead to higher wages.
“Welders make more money than philosophers. We need more welders and less philosophers,” he said, to one of the night’s loudest cheers in blue-collar Wisconsin.
