Deep differences among the candidates over everything from immigration to the use of military force were exposed at Tuesday’s Republican primary debate, where front-runners Donald Trump and Ben Carson often had to cede the spotlight to a full stage of spirited competitors.

Even Jeb Bush, who has struggled for airtime during past face-offs, was able to elbow his way into the fray, taking shots at President Obama’s economic record and Trump’s immigration plan.

“They’re doing high fives in the Clinton campaign right now when they hear this,” Bush said, of Trump’s call to deport millions.

Whether Bush, the former Florida governor who has steadily slid in the polls since losing his summer front-runner status, can regain momentum is an open question. And he was hardly alone among the middle-tier candidates asserting their policies on stage at the Fox Business Network/Wall Street Journal debate in Milwaukee. 

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One of the biggest wedges was over the U.S. military.

Kentucky Sen. Rand Paul held his ground in vociferously calling for reining in the military budget and avoiding foreign military interventions. For this, he drew sharp rebukes from Florida Sen. Marco Rubio, former HP CEO Carly Fiorina and others. 

“I know that Rand is a committed isolationist. I’m not,” Rubio said.

Paul countered that spending on defense is driving up the debt and making America “less safe.”

“I want a strong national defense, but I don’t want us to be bankrupt,” he said.

This snowballed into a heated debate over Russia’s mounting intervention in the Middle East.

When Trump suggested the U.S. cannot be the world’s policeman, Bush said “he is absolutely wrong on this” and the U.S. needs to be the “world’s leader.” 

Fiorina said both Trump and Paul should know that “we should not speak to people from a position of weakness.” In a stand-out moment, Fiorina rattled off her plans for countering Putin’s profile, including rebuilding the missile defense system in Poland, launching military exercises in the Baltic states and perhaps putting thousands of troops in Germany.

The U.S. needs to have the “strongest military on the planet and everyone has to know it,” she said.

“You can be strong without being involved in every civil war in the world,” said Paul, not backing down.

When Fiorina tried to interject, Trump scolded her – saying, “Why does she keep interrupting everybody?” – but was booed by the audience. 

Rubio added that Putin is a “gangster” who understands “only geopolitical strength.”

The debate was the fourth for the GOP field and the last debate until mid-December, putting pressure on the candidates to seek a breakout moment before the holiday lull.

Unlike the most recent debate, where candidates sparred frequently with the moderators, the candidates on Tuesday mostly stuck to policy issues. 

The immigration debate also drove a wedge into the field as Trump tussled with his GOP rivals over his plan to deport millions of illegal immigrants.

As he has at past debates, the billionaire businessman repeated his plan to build a U.S.-Mexico border wall. And when asked whether he’d deport the millions in the country illegally, he said, “We have no choice.”

“We either have a country or we don’t have a country,” Trump said, adding that some of those deported could return.

The comment quickly drew in Ohio Gov. John Kasich, who said, “Think about the families.”

He said illegal immigrants should pay a penalty, but called Trump’s plan a “silly argument” and “not an adult argument.”

After Kasich continued to slam the plan, Trump cited his own business record and said: “I don’t have to hear from his man.”

But Bush backed up Kasich and said Trump’s plan would “tear communities apart.”

Texas Sen. Ted Cruz, though, sided with Trump. He said Democrats indeed are laughing, “Because if Republicans join Democrats as the party of amnesty, we will lose.”

He also quipped, “If a bunch of people with journalism degrees were coming over and driving down wages in the press, then we would see stories about the economic calamity that is befalling our nation.”

The debate otherwise focused in large part on economic and fiscal issues, and the candidates used the opportunity to flag big government as a central problem holding the economy back.

Bush called for repealing “every rule” the administration has in progress.

“Start over,” he said, citing the EPA’s Clean Power Plan and other regulations.

Cruz said “the Obama economy is a disaster” but the economy could improve with tax and regulatory reform.

He called for “pulling back the armies of regulators that have descended like locusts on small businesses.”

At the opening of the debate, the two front-running Republican candidates, Trump and Carson, also said they would not raise the minimum wage, warning that would hurt the economy in the long run.

Trump and Carson were asked at the outset about protesters demanding a $15 minimum wage. Trump said while he hates to say it, “We have to leave it the way it is.”

He acknowledged Americans would have to work hard to “get into that upper strata,” but “I would not raise the minimum.”

Carson, the retired neurosurgeon, said raising the minimum wage would increase the number of jobless. He said the real issue is, “How do we allow people to ascend the ladder of opportunity rather than how do we give them everything and keep them dependent?”

He said, “I would not raise it.”

Rubio also chimed in, saying raising the wage would “make people more expensive than a machine.”

The eight candidates faced off Tuesday at a time of tense sparring within the field’s top tiers.

Trump used an Illinois rally the night before to hammer rival Carson over violent incidents during his youth and question why he’s doing well in the polls. Carson, for his part, has spent the last several days sparring with the media and his rivals over reports questioning his personal story. 

At the debate, he was asked about some of that coverage.

“I have no problem with being vetted … What I do have a problem with is being lied about,” Carson said.

He suggested Democrats don’t face the same treatment, and citing Hillary Clinton’s faulty narrative about the Benghazi terror attack said, “Where I come from, they call that a lie.”

Cruz stumbled at one point during Tuesday’s debate. In a moment reminiscent of Rick Perry’s infamous debate gaffe in the 2012 primary campaign, Cruz said he wanted to dismantle five agencies but listed Commerce twice.

The prime-time event followed an earlier debate with lower-polling candidates, where New Jersey Gov. Chris Christie repeatedly hammered Clinton as well.