Jeb Bush and Rand Paul stood out as the fourth Republican presidential debate revealed deep philosophical splits in the GOP, especially on the subjects of foreign policy and immigration.

Tuesday’s debate was one of the most substantive yet, with candidates delving deeply into their presidential plans, the Washington Post reported, stating that the event featured standout performances by two candidates who needed them: Bush and Paul. Some of the more prominent candidates, such as Donald Trump and Ben Carson, took a backseat, and Ted Cruz made a Rick Perry-esque error as he stated a plan to eliminate five federal agencies but named just four, twice naming the Department of Commerce in his list.

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One of Tuesday night’s sharpest clashes was over immigration and the prospect of deporting millions of people who entered the United States illegally, a related New York Post article reported.

“You are going to have to send people out. Look, we’re a country,” said Donald Trump, when asked about the prospect of mass deportations, prompting Ohio Gov. John Kasich, the most aggressive candidate on the stage, according to the New York Post, to say there was no way to ship 11 million people to Mexico. “It is not an adult argument,” he said about Trump's plan.

Another contentious exchange concerned America’s foreign policy as Trump advocated a more isolationist strategy. “If Putin wants to go and knock the hell out of ISIS, I am all for it,” Trump said, claiming the United States should not get involved militarily against the Islamic State, the Washington Post reported. 

“Be ready to send your sons and daughters to another war in Iraq,” Sen. Paul warned, drawing a chorus of disagreement from candidates Cruz, Rubio and Fiorina, who all advocated for a stronger, more aggressive American stance abroad, the New York Post reported.

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Ben Carson, who has recently faced criticism over several of the claims he has made about his past, was quoted by the Washington Post: “Thank you for not asking me what I said in the 10th grade. … I have no problem with being vetted. What I do have a problem with is being lied about. And putting that out there as truth."