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GOP hopefuls trade barbs on immigration issues

Republican presidential candidates clashed over tax policy, military spending and immigration Tuesday night at a televised debate focused on economic issues.

MILWAUKEE -- Republican presidential candidates clashed over tax policy, military spending and immigration Tuesday night at a televised debate focused on economic issues.

The two-hour program, hosted by Fox Business Network, was a particularly high-profile outing for Jeb Bush, the former Florida governor whose standing in the polls has plunged after several disappointing appearances on the debate stage. Retired neurosurgeon Ben Carson also found himself in the spotlight, addressing the scrutiny of past biographical statements that has accompanied his rise in national polls and in Iowa, the first in the nation caucus state.

RELATED: Carson laughs off biographical scrutiny

Front-runner Donald Trump and Texas Sen. Ted Cruz pushed a hard crackdown on illegal immigration, which Bush and Ohio Gov. John Kasich warned would be an economic and political disaster for the U.S. if 11 million undocumented immigrants were forcibly deported.

Trump, who has staked much of his campaign on a plan to send undocumented immigrants back home, reiterated his pledge to build a wall across the southern U.S. border that Mexico would pay for. “The wall will be built. The wall will be successful,” Trump said, sidestepping questions on specifically how he would deport millions of people living illegally in the U.S.

Trump’s words drew immediate criticism from Kasich, who called the plan a “silly argument.” Bush, who had struggled to break through in the discussion, sided quickly with Kasich, warning the discussion was playing into Democrats’ hands.

"They are doing high-fives in the Clinton camp when they hear this,” Bush said, criticizing Trump’s deportation plan as not “embracing American values.”

Cruz battled back, aligning with Trump.

"The Democrats are laughing because if Republicans join Democrats as the party of amnesty we will lose," Cruz said. 

RELATED: Trump hails immigration setback

Cruz added that the "politics of it would be very different if a bunch of lawyers and bankers were crossing the Rio Grande or if a bunch of people with journalism degrees were driving down the wages of the press."

Conservative critics of immigration often claim migrants depress income, but Cruz has called for allowing significantly more high-skilled immigrants and criticized Florida Sen. Marco Rubio's Senate bill for not going far enough on that front. 

Carson, who has batted back questions about whether he embellished stories of his violent boyhood and if he was offered a scholarship to the U.S. Military Academy at West Point, reoriented the issue of truthfulness to Democratic front-runner Hillary Clinton.

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“I look at Hillary Clinton who sits there and tells her daughter and a government official that this is terrorist attack tells everybody else it was a vide they call that a lie,” Carson said, raising questions about Clinton’s handling of the terrorist attacks on the American consulate in Benghazi, Libya.

Rubio, who performed strongly in the previous debate, faced his toughest challenge yet onstage as Kentucky Sen. Rand Paul accused him of betraying conservatism by offering a refundable child tax credit and calling for higher military spending.

“You cannot be a conservative if you’re going to keep promoting new programs you’re not going to pay for,” Paul said.

Rubio defended his tax plan, saying it would help encourage more stable families and upward mobility, and shot back at Paul on foreign policy.

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

International affairs did take a prominent role in the forum, as candidates weighed in on a possible no-fly zone in Syria and the prospect of tangling with Russian strongman Vladimir Putin over Syria. Trump and Paul adopted a more dovish posture, while Rubio, Bush and Fiorina advocated a more aggressive stand overseas.

Rubio called Putin "a gangster," while Trump said he had appeared on "60 Minutes" with the Russian leader and would know how to work with him. 

"If Putin wants to knock the hell out of ISIS, I'm all for it 100 percent and I can't understand how anybody would be against that," Trump said. 

Bush pushed back on Trump, who argued that it wasn't the job of the U.S. to police the Middle East. “Donald is wrong on this," Bush said. 

Businesswoman Carly Fiorina chided Trump, saying she had met Putin "not in a green room for a show, but in a private meeting." Fact checkers noted that Fiorina did meet Putin in a green room before a 2001 conference in China.

Fiorina went on to press for an aggressive posture against Russia that includes a troop buildup in Europe. 

Most of the candidates have put out multi-trillion dollar tax plans that slash taxes across the board while tilting benefits towards the wealthy and businesses. Bush, Rubio, Kasich, and Trump have proposed lowering top tax rates for individuals and businesses while candidates like Paul, Carson, and Cruz have suggested a flat tax in which all Americans pay a similar rate on income.

Carson has offered the fewest details on his plan, but dropped a major one on Tuesday when he said he would scrap the home mortgage deduction — a position unique within the field. 

"The fact of the matter is people had homes before 1913 when we introduced federal income tax and later after that," Carson said. 

Cruz, for his part, said he would "absolutely not" bail out big banks -- saying he would let Bank of America fail if it were on the brink.

Fouhy reported from New York. NBC News contributed to this report.