Another source of friction at the debate in Milwaukee was foreign policy.
The eight candidates were divided on whether the US 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 US-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.
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