Trump’s immigration plan savaged by rivals
His hardline proposal was attacked as impractical and divisive by John Kasich and Jeb Bush, who are also running for the Republican presidential nomination.
Mr Trump, a billionaire New Yorker who has been leading in the polls, was booed as he tried to counter-attack.
Another source of friction at the debate in Milwaukee was foreign policy.
The eight candidates were divided on whether the U.S. should do more to intervene in the Middle East, especially in the fight against Islamic State militants.
But immigration sparked the biggest confrontation, when Mr Trump said a wall should be built at the U.S-Mexico border and all migrants living illegally in the US must be deported.
This was met with disdain by Mr Kasich, the governor of Ohio.
“Come on, folks, we all know you can’t pick them up and ship them back across the border. It’s a silly argument. It’s not an adult argument.”
Mr Bush, the former Florida governor, said it would tear families apart and played into the hands of Democratic frontrunner Hillary Clinton.
The debate, hosted by Fox Business, began by talking about raising the minimum wage, which several candidates opposed.
Jeb Bush, who was more forceful than in previous debates, said that Hillary Clinton’s campaign would be doing high-fives because Mr Trump’s hardline stance on immigration threatened to alienate Latino voters, a fast-growing demographic.
Mr Trump was also booed when he asked of the only woman on stage, the former executive Carly Fiorina, “why does she keep on interrupting everyone?”